D, Embryo with lateral torsion and an endogastric shell.
Such cannulated cells are characteristic of the nephridia of many worms, and the organs thus formed in the embryo Limnaeus are embryonic nephridia.
If we go back to the first instance cited, the embryo in the seed and its development during germination, we can ascertain what is necessary for its life by inquiring what are the materials which are deposited in the seed, and which become exhausted by consumption as growth and development proceed.
After fertilization the female cell, now called the oospore, divides and part of it develops into the embryo (new sporophyte), which remains dormant for a time still protected by the ovule which has developed to become the seed.
The name expresses the most universal character of the class, the importance of which was first noticed by John Ray, namely, the presence of a pair of seed-leaves or cotyledons, in the plantlet or embryo contained in the seed.
It is absurd to call the larva of a newt or of a Caecilian a tadpole, nor is the free-swimming embryo of a frog as it leaves the egg a tadpole.
C, Embryo with ventral flexure and exogastric shell.
B, Embryo with ventral flexure of the intestine.
The rows of cells from which the laticiferous vessels are formed can be distinguished in many cases in the young embryo while still in the dry seed (Scott), but the latex vessels in process of formation are more easily seen when germination has begun.
The seeds are minute and innumerable; they contain a small rudimentary embryo surrounded by a thin loose membraneous coat, and are scattered by means of hygroscopic hairs on the inside of the valves which by their movements jerk out the seeds.
The preconchylian invagination or shell-gland is formed in the embryo behind the velum, on the surface opposite the blastopore.
areas are found on the foot of the embryo Pulmonate Limax and on the yolk-sac (distended foot-surface) of the Cephalopod Loligo.
The body thus formed ment of is called the embryo, and this develops into the adult Primary plant, not by continued growth of all its parts as in an animal, but by localization of the regions of cell-division and growth, such a localized region being called a growing-point.
In cases where the development of the embryo is advanced at the resting period, traces run from the cotyledons and determine the symmetry of the stele of the primitive axis, the upperpart of which often shows stem-structure, in some respects at least, and is called the hypocoty- ledonary stem or hypocotyl, while the lower part is the primary root .~-,
When the young sporophyte first begins its independent lifewhen, that is, it exists in the form of the embryo in the seedits living substance has no power of utilizing the simple inorganic compounds spoken of.
In the case of the great grey kangaroo, for instance, the period of gestation is less than forty days, and the newly-born embryo, which is blind, naked, and unable to use its bud-like limbs, is little more than an inch in length.
- Embryo of Cavolinia tridentate.
The embryo consists of an axis bearing two or more cotyledons and ending below in a radicle; it lies in a generally copious food-storing tissue (endosperm) which is the remains of the female prothallus.
The embryo of a moth, a dragon-fly point.
(After Robert.) A, Embryo without flexure.
When the middle and hinder regions of the blastopore are closing in, an equatorial ridge of ciliated cells is formed, converting the embryo into a typical trochosphere.
Chun and Woltereck, on the other hand, regard the stem as a stolo prolifer arising from the aboral pole, that is to say, from the ex-umbrella, similar to that which grows out from the ex-umbral surface of the embryo of the Narcomedusae and produces buds, a view which is certainly supported by the embryological evidence to be adduced shortly.
size compared with the thorax or abdomen, but in the embryo it On the whole it seems likely that the endoderm is represented in forms a much larger portion of the body than it does in the adult.
It is absent in the Ratitae, which from this feature have received their name, but considerable traces of a cartilaginous keel occur in the embryo of the ostrich, showing undeniably that the absence of a keel in the recent bird is not a primitive, fundamental feature.
The foot is always simple, with its flat crawling surface extending from end to end, but in the embryo Limnaea it shows a bilobed character, which leads on to the condition characteristic of Pteropoda.
- Embryo of Limnaeus stagnalis, at a stage when the Trochosphere is developing foot and shell-gland and becoming a Veliger, seen as a transparent object under slight pressure.
The Pulmonata have a straight visceral nerve-loop, usually no operculum even in the embryo, and a multidenticulate radula, the teeth being equi-formal; and they are hermaphrodite.
If the three principal organ-systems of the medusa, namely mouth, tentacles and umbrella, be considered in the light of phylogeny, it is evident that the manubrium bearing the mouth must be the oldest, as representing a common property of all the Coelentera, even of the gastrula embryo of all Enterozoa.
and of the muscid flies, an anterior and a posterior endodermThe embryo thus becomes transferred to the dorsal face of the egg, rudiment both derived from the " endoblast " become apparent but at a later stage it undergoes reversion to its original ventral at an early stage, in close association with the stomodaeum and position.
It has been ascertained that the nephridia of Oligochaeta are preceded in the embryo by a pair of delicate and sinuous tubes, also found in the Hirudinea and Polychaeta, which are larval excretory organs.
If the embryo is set free as a free-swimming, so-called planula-larva, in the blastula, parenchymula, or gastrula stage, then a free actinula stage is not found; if, on the other hand, a free actinula occurs, then there is no free planula stage.
It is not true, for example, that a fish is a reptile arrested in its development, or that a reptile was ever a fish; but it is true that the reptile embryo, at one stage of its development, is an organism which, if it had an independent existence, must be classified among fishes; and all the organs of the reptile pass, in the course of their development, through conditions which are closely analogous to those which are permanent in some fishes.
The female is viviparous, and the young, which, unlike the parent, are provided with a long tail, live free in water; it was formerly believed from the frequency with which the legs and feet were attacked by this parasite that the embryo entered the skin directly from the water, but it has been shown by Fedschenko, and confirmed by Manson, Leiper and others, that the larva bores its way into the body of a Cyclops and there undergoes further development.
In fact, there is a period when, as Aristotle long ago said, the embryo of the highest animal has the form of a mere worm, and, devoid of internal and external organization, is merely an almost structureless lump of polype-substance.
He showed that all the organs of plants are built up of cells, that the plant embryo originates from a single cell, and that the physiological activities of the plant are dependent upon the individual activities of these vital units.
In germination of the seed the root of the embryo (radicle) grows out to get a holdfast for the plant; this is generally followed by the growth of the short stem immediately above the root, the so-called "hypocotyl," which carries up the cotyledons above the ground, where they spread to the light and become the first green leaves of the plant.
The external form of the embryo goes through the same changes as in other Gastropods, and is not, as was held previously to Lankester's observations, exceptional.
the seed contains a large hooked embryo.
By this time the embryo has all the organs of the adult perfected save only the reproductive; these develop only when the first host is swallowed by the second or final host, in which case the parasite attaches itself to the wall of the alimentary canal and becomes adult.
The seeds are filled with the large embryo, the two cotyledons of which are variously folded.
A, Larva which has just left brood-pouch; B, longitudinal section through a somewhat later stage; C, the fully formed embryo just before fixing - the neo-embryo of Beecher.
Cuscuta has a thread-like, spirally twisted embryo with no trace of cotyledons.
The germ band evidently marks the ventral aspect of the developing insect, whose body must be completed by the extension of the embryo so as to enclose the yolk dorsally.
The embryo consists of an axis bearing one (Monocotyledons) or two (Dicotyledons) cotyledons, which protect the stem bud (plumule) of the future plant, and ending below in a radicle.
In the seed-forming plants (Phanerogams) one or more primary leaves (cotyledons) are already formed in the resting embryo.
Lecaillon (1898) on various leaf beetles, tend to show that the organ " in the embryos of the lower Arthropoda corresponds with whole of the " mid-gut " arises from the proliferation of cells at the the region invaginated to form the serosa of the hexapod embryo.
- Cross section of Embryo of German Cockroach (Phyllo- labrum represent, as already said, an unpaired median outgrowth dromia).
or " vertex," the compound eyes and the front divisions of the genae are formed by the cephalic lobes of the embryo (belonging membrane analogous to the amnion of higher Vertebrates andto the ocular segment), while the mandibular and maxillary segments known by the same term.
They do not long persist in the embryo, but disappear, and the area each one occupied becomes part of the sternite.
The ganglia become greatly changed in position during the later life, and it is usually said that there are only ten pairs of abdominal ganglia even in the embryo.
- Morphology of an Insect: the embryo of Gryllotalpa, somewhat diagrammatic. The longitudinal segmented band along the middle line represents the early segmentation of the nervous system and the subsequent median field of each sternite; the lateral transverse unshaded bands are the lateral fields of each segment; the shaded areas indicate the more internally placed mesoderm layer.
- Embryo of scorpion, ventral view showing somites and appendages.
- Portion of a similar embryo at a later stage of growth.
- Section through an early embryo of Limulus longispina, showing seven transverse divisions in the region of the unsegmented anterior carapace.
The prae-genital somite, after appearing in the embryo, either is obliterated (Scorpio, Galeodes, Opilio and others) or is retained as a reduced narrow region of the body, the " waist," between prosoma and mesosoma.
6, 3); the seeds contain a small embryo in a copious fleshy or cartilaginous endosperm.
Embryo taken out of seed.
Weismann has also ingeniously argued from the structure of the egg-cell and sperm-cell, and from the way in which, and the period at which, they are derived in the course of the growth of the embryo from the egg - from the fertilized egg-cell - that it is impossible (it would be better to say highly improbable) that an alteration in parental structure could produce any exactly representative change in the substance of the germ or sperm-cells.
The female gametophyte is extremely reduced; there is a sexual apparatus of naked cells, one of which is the egg-cell which, after fusion with a male cell, divides to form a large siispensorial cell and a terminal embryo.
In moths and certain saw-flies there is no rupture of the membranes; the Russian zoologists Tichomirov and Kovalevsky have described the growth of both amnion and embryonic ectoderm around the yolk, the embryo being thus completely enclosed until hatching time by both amnion and serosa.
In the cockroach embryo, before the segmentation of the germ-band has begun, the primitive germ-cells can be recognized at the hinder end of the mesoderm, from whose ordinary cells they can be distinguished by their larger size.
The presence of rudiments of the genital ducts of both sexes in the embryo of either sex is interesting and suggestive.
- Cross sections through Abdomen of German Cockroach Embryo.
Hence we are inclined to look on the imaginal disks as cellular areas that possess in a latent condition the powers of growth and development that exist in the embryo, powers that only become evident in certain special conditions of the organism.
In the egg of these insects a small number of nuclei are formed by the division of the nucleus, and each of these nuclei originates by division the cell-layers of a separate embryo.
Aristotle and Harvey (De generatione animalium, 1651) had considered the insect larva as a prematurely hatched embryo and the pupa as a second egg.
Weismann (1863-1864) traced details of the growth of embryo and of pupa among the Diptera, and A.
In the embryo, however, what have been regarded as remnants of limbs may be seen.
The embryo thus passes from the body of the female into the alimentary canal of the host and leaves this with the faeces.
In 1893, some years after the identification of the somites of Limulus with those of Scorpio, thus indicated, had been published, zoologists were startled by the discovery by a Japanese zoologist, Kishinouye (8), of a seventh prosomatic somite in the embryo of Limulus longispina.
In the case of Scorpio this segment is indicated in the embryo by the presence of a pair of rudimentary appendages, carried by a well-marked somite.
Previously to this, Lankester's pupil Gulland had shown (1885) that in the embryo the coxal gland is a comparatively simple tube, which opens to the exterior in this position and by its other extremity into a coelomic space.
Cohnheim's hypothesis of " embryonic residues " provides that early in the development of the embryo some of the cells, or groups of cells, are separated from their organic continuity during the various foldings that take place in the actively growing embryo.
Then we have Beard's " germ-cell " hypothesis, in which he holds that many of the germ-cells in the growing embryo fail to reach their proper position - the generative areas - and settle down and become quiescent in some somatic tissue of the embryo.
Some workers regard certain appearances in dividing cells found in cancer as evidence of a reversion of the somatic cell to the germcell type (heterotypical), otherwise found only in the process which results in the formation of an embryo.
This fact gave rise in ancient times to the false idea that the tapeworm originated from the union of these segments; and in modern times it has led to the view that the tapeworm is not a segmented organism (the monozoic view), but is a colony composed of the scolex which arises from the embryo and of the proglottides, which are asexually produced buds that, upon or before attaining their full size and maturity, become separated, grow, and, in some cases, live freely for a time, just as the segments of a strobilating jelly-fish grow, separate and become sexual individuals (the polyzoic view).
The embryo is provided with ten hooks, and appears to select Lamellibranchs (Mactra) for its intermediate host.
G, six-hooked embryo, highly magnified.
The egg gives rise in the uterus to a six-hooked embryo, which reaches the first host in a variety of ways.
In this way bladders as large as an orange and containing secondary bladders, A each with a scolex, may arise from a single embryo.
D, ciliated embryo of B.
The development of the six-hooked embryo or " oncho FIG.
(c) forms the body of the embryo, (b) and (d) enclose it and form a covering.
The embryo undergoes differentiation into an outer layer of cells that produce a chitinoid coat, a middle layer of cells, and a central spherical hexacanth body closely enveloped by the middle coat.
Arrived in the intestine of the intermediate host, the hooked embryo is set free and works its way to some distant site.
A, the six-hooked embryo.
On this view, therefore, at least two asexual generations (embryo and scolex) alternate with a sexual one (proglottides); and in the case of Staphylocystis the cyst contains two asexually produced generations, so that in such forms three stages (embryo, primary scolex-buds, secondary scolices) intervene between the proglottis of a Cestode and that of its offspring.
On this view, multiple scolices are, therefore, not buds, but an example of the unlocalized organization of the embryo such as occurs in other groups of animals, and is demonstrated by experiment.
In North Germany the mature tapeworm was found on post-mortem examination once in every 200 bodies examined, while its embryo, the Cysticercus cellulosae, was found in in every 76 bodies.
In the Taenia solium it takes 3 to 3z months from the time of ingestion of the embryo to the passage of the matured segments, but in the Taenia saginata the time is only about 60 days.
The eggs are comparatively few, and development is direct, the embryo after reaching its host remaining attached to it for life.
Gyrodactylus produces only one large egg at a time and this develcps in situ into an embryo: but within this embryo another appears before the first leaves the parent.
This anomalous phenomenon is still obscure, for we do not yet know whether the second embryo is developed sexually or asexually from the first.
If the egg with its contained embryo falls into water E (All from Marshall and Hurst, after Thomas.) FIG.
The ovicells are modified zooecia, and contain numerous embryos which in the cases so far investigated arise by fission of a primary embryo developed from an egg.
The ovicells commonly found as globular swellings surmounting the orifices are not direct modifications of zooecia, and each typically contains a single egg or embryo.
In the Cyclostomata the primary embryo undergoes repeated fission without developing definite organs, and each of the numerous pieces so formed becomes a free larva, which possesses no alimentary canal.
None the less it is easy to find it in embryo in the speculations of the essentially European philosophers of Greece.
In some families, as many freshwater snakes, the sea snakes, Viperinae and Crotalinae, the eggs are retained in the oviduct until the embryo is fully developed.
When ripe the two carpels separate in the form of two valves and liberate a large number of seeds, each provided at the base with a tuft of silky hairs, and containing a straight embryo without any investing albumen.
The female lays her egg in the egg of a small ermine moth (Hyponomeuta) and the egg gives rise not to a single embryo but to a hundred, which develop as the host-caterpillar develops, being found at a later stage within the latter enveloped in a flexible tube.
Buonanni, a learned Jesuit of Rome) that they are not generated out of the mud or sand found on the seashore or the beds of rivers at low water, but from spawn, by the regular course of generation; and he maintained the same to be true of the fresh-water mussel (Unio), whose ova he examined so carefully that he saw in them the rotation of the embryo, a phenomenon supposed to have been first discovered long afterwards.
The general view was, that the embryo originated in the ovule, which was in some obscure manner fertilized by the pollen.
C. Treviranus, professor of botany in Bonn, roused the attention of botanists to the development of the embryo, but although he made valuable researches, he did not add much in the way of new information.
The whole subject of fertilization and development of the embryo has been more recently investigated with great assiduity and zeal, as regards both cryptogamous and phanerogamous plants, and details must be sought in the various special articles.
(3) The generative cells are produced in either the ectoderm or endoderm, and not in a third layer arising in the embryo, distinct from the two primary layers; in other words, there is no mesoderm or coelom.
After the gastrula stage, which is found as a developmental stage in all Enterozoa, the embryo of the Hydrozoa proceeds to develop characters which are peculiar to the Coelen- a terata only.
The internal structural differences are even more characteristic. In the hydropolyp the blastopore of the embryo forms the adult mouth situated at the extremity of the hypostome, and the ectoderm and FIG.
Great apparent differences may also be brought about by variations in the period at which the embryo is set free as a larva, and since two free-swimming stages, planula and actinula, are unnecessary, one or other of them is always suppressed.
In Cordylophora the embryo is set free at the parenchymula stage as a planula which fixes itself and develops into a polyp, both gastrula and actinula stages being suppressed.
maculosa, but as a rule only one fully develops in each uterus, the embryo being nourished on the yolk of the other eggs, which more or less dissolve to form a large mass of nutrient matter.
The embryo passes through three stages - (I) still enclosed within the egg and living on its own yolk; (2) free, within the vitelline mass, which is directly swallowed by the mouth; (3) there is no more vitelline mass, but the embryo is possessed of long external gills, which serve for an exchange of nutritive fluid through the maternal uterus, these gills functioning in the same way as the chorionic villi of the mammalian egg.
Many lizards, however, retain the eggs in the oviducts until the embryo is fully developed; these species then bring forth living young and are called ovo-viviparous by purists.
Flowering plants bear a seed containing an embryo, with usually one or two cotyledons, or seed-leaves; while in flowerless plants there is no seed and therefore no true cotyledon.
The embryo of the taenia echinococcus finds its way from the stomach or intestine into a vein passing to the liver, and, settling itself in the liver, causes so much disturbance there that a capsule of inflammatory material forms around it.
Inside this wall is the special covering of the embryo which shortly becomes distended with clear hydatid fluid.
In many embryo Lamellibranchs a centro-dorsal primitive shell-gland or follicle has been detected.
The embryo is now ec, Ectoderm.
C, Similar optical section at a E, Surface view of an embryo at little later stage.
the blastopore is now more F, Later embryo seen as a transcontracted, d; and cells, me, m, Mouth.
The embryo has be found here in thousands in the increased in size by accumulasummer and autumn months.
- B, Same embryo as fig.
24, in optical median section, showing the invaginated cells hy which form the arch-enteron, and the mesoblastic cells me which are budded off from the surface of the mass hy, and apply themselves to the inner surface of the epiblastic cell-layer cp. C, The same embryo focused so as to show the mesoblastic cells which immediately underlie the outer cell-layer.
- Surface view of a forty-five hour embryo of Yoldia limatula.
- Diagram of Embryo of Pisidium.
While the soul is propagated, like any other essence, by the efficient, which is the seed, to the matter, which is the germ, of the embryo man, intellect alone enters from without (Obpa6Ev), and is alone divine (BEiov, not 6EOS), because its activity communicates with no bodily activity (De Gen.
It must, of course, be understood that the germinal epithelium covering the ridge, and the mesenchyme inside it, are both derived from the mesoderm or middle layer of the embryo.
- Transverse Section through a Rat Embryo a.
In the Dibranchia true nephridia have not been detected in the embryo, nor has it been shown that the genital ducts are derived from the renal tubes.
The blastopore, together with the whole embryo, now elongates.
The external form of the embryo meanwhile passes through highly characteristic changes, which are on the whole fairly constant ara (After Lankester, 17.) FIG.
A circlet of cilia forms when the embryo is still nearly spherical in an equatorial position.
The embryo generally fills the seed, and the cotyledons are rolled or folded on each other.
The reproduction of the higher plants takes place either asexually by the formation of buds or organs answering thereto, or sexually by the production of an embryo plant within the seed.
Germination is often slower where there is a store of available food in the perisperm, or in the endosperm, or in the embryo itself, than where this is scanty or wanting.
A large distinct leafy embryo lies in the middle of a dense, oily tissue (endosperm).
By the development of a ciliated ring just in front of the mouth the embryo becomes a trochosphere.
In other species the infection occurs through the style of the flower, but the fungus after reaching the ovule develops no further during that year but remains dormant in the embryo of the seed.
From the historical point of view it may be suggested that neither North nor South was correct in theory in 1861: the United States were not a nation; neither were the states sovereign; but from the embryo political communities of 1776-1787, in which no proper sovereignty existed anywhere, two nationalities were slowly being evolved and two sovereignties were in the making; the North and the South each fulfilled most of the requirements for a nation and they were mutually unlike and hostile.
The development of the embryo within the egg takes about three weeks.
The resemblance of Dinophilus to the Rotifera is, however, quite superficial, and the general structure of this genus with distinct traces of segmentation, especially in the embryo, points to its close affinity, if not to Polygordius in particular, at all events to the Annelida.
The greatest merit of this book is the use of the number of cotyledons as a basis of classification; though it must be remembered that the difference between the monocotyledonous and dicotyledonous embryo was detected by Nehemiah Grew.
This remarkable double fertilization as it has been called, although only recently discovered, has been proved to take place in widely-separated families, and both in Monocotyledons and Dicotyledons, and there is every probability that, perhaps with variations, it is the normal process in Angiosperms. After impregnation the fertilized oosphere immediately surrounds itself with a cell-wall and becomes the oospore which by a process of growth forms the embryo of the new plant.
The endosperm-nucleus divides rapidly to produce a cellular tissue which fills up the interior of the rapidly-growing embryosac, and forms a tissue, known as endosperm, in which is stored a supply of nourishment for the use later on of the embryo.
If, on the other hand, the endosperm is the product of an act of fertilization as definite as that giving rise to the embryo itself, we have to recognize that twin-plants are produced within the embryo-sac - one, the embryo, which becomes the angiospermous plant, the other, the endosperm, a short-lived, undifferentiated nurse to assist in the nutrition of the former, even as the subsidiary embryos in a pluri-embryonic Gymnosperm may facilitate the nutrition of the dominant one.
If this is so, and the endosperm like the embryo is normally the product of a sexual act, hybridization will give a hybrid endosperm as it does a hybrid embryo, and herein (it is suggested) we may have the explanation of the phenomenon of xenia observed in the mixed endosperms of hybrid races of maize and other plants, regarding which it has only been possible hitherto to assert that they were indications of the extension of the influence of the pollen beyond the egg and its product.
The antipodal cells aid more or less in the process of nutrition of the developing embryo, and may undergo multiplication, though they ultimately disintegrate, as do also the synergidae.
a pro-embryo - a cellular row of which the cell nearest the micropyle becomes attached to the apex of the embryo-sac, and thus fixes the position of the developing embryo, while the terminal cell is projected into its cavity.
In Dicotyledons the shoot of the embryo is wholly derived from the terminal cell of the pro-embryo, from the next cell the root arises, and the remaining ones form the suspensor.
In many Monocotyledons the terminal cell forms the cotyledonary portion alone of the shoot of the embryo, its axial part and the root being derived from the adjacent cell; the cotyledon is thus a terminal structure and the apex of the primary stem a lateral one - a condition in marked contrast with that of the Dicotyledons.
The primary root of the embryo in all Angiosperms points towards the micropyle.
The developing embryo at the end of the suspensor grows out to a varying extent into the forming endosperm, from which by surface absorption it derives good material for growth; at the same time the suspensor plays a direct part as a carrier of nutrition, and may even develop, where perhaps no endosperm is formed, special absorptive "suspensor roots" which invest the developing embryo, or pass out into the body and coats of the ovule, or even into the placenta.
In some cases the embryo or the embryo-sac sends out suckers into the nucellus and ovular integument.
As the embryo develops it may absorb all the food material available, and store, either in its cotyledons or in its hypocotyl, what is not immediately required for growth, as reserve-food for use in germination, and by so doing it increases in size until it may fill entirely the embryo-sac; or its absorptive power at this stage may be limited to what is necessary for growth and it remains of relatively small size, occupying but a small area of the embryo-sac, which is otherwise filled with endosperm in which the reserve-food is stored.
The position of the embryo in relation to the endosperm varies, sometimes it is internal, sometimes external, but the significance of this has not yet been established.
Its segmentation always begins before that of the egg, and thus there is timely preparation for the nursing of the young embryo.
If in its extension to contain the new formations within it the embryo-sac remains narrow, endosperm formation proceeds upon the lines of a cell-division, but in wide embryo-sacs the endosperm is first of all formed as a layer of naked cells around the wall of the sac, and only gradually acquires a pluricellular character, forming a tissue filling the sac. The function of the endosperm is primarily that of nourishing the embryo, and its basal position in the embryo-sac places it favourably for the absorption of food material entering the ovule.
Its duration varies with the precocity of the embryo.
It may be wholly absorbed by the progressive growth of the embryo within the embryo-sac, or it may persist as a definite and more or less conspicuous constituent of the seed.
In cases where the embryo has stored reserve food within itself and thus provided for self-nutrition, such endosperm as remains in the seed may take on other functions, for instance, that of water-absorption.
Parthenogenesis, or the development of an embryo from an egg-cell without the latter having been fertilized has been described in species of Thalictrum, Antennaria and Alchemilla.
Isolated cases show that any of the cells within the embryo-sac may exceptionally form an embryo, e.g.
In two Malayan species of Balanophora, the embryo is developed from a cell of the endosperm, which is formed from the upper polar nucleus only, the egg apparatus becoming disorganized.
As the development of embryo and endosperm proceeds within the embryo-sac, its wall enlarges and commonly absorbs the substance of the nucellus (which is likewise enlarging) to near its outer limit, and combines with it and the integument Fruit and to form the seed-coat; or the whole nucellus and even the integument may be absorbed.
The presence or absence of endosperm, its relative amount when present, and the position of the embryo within it, are valuable characters for the distinction of orders and groups of orders.
Their function is the twofold one of protecting the embryo and of aiding in dissemination; they may also directly promote germination.
If the fruit is a dehiscent one and the seed is therefore soon exposed, the seed-coat has to provide for the protection of the embryo and may also have to secure dissemination.
On the other hand, indehiscent fruits discharge these functions for the embryo, and the seed-coat is only slightly developed.
Their fortuitous dissemination does not always bring seeds upon a suitable nidus for germination, the primary essential of which is a sufficiency of moisture, and the duration of vitality of the embryo is a point of interest.
This pause, often of so long duration, in the growth of the embryo between the time of its perfect development within the seed and the moment of germination, is one of the remarkable and distinctive features of the life of Spermatophytes.
The aim of germination is the fixing of the embryo in the soil, effected usually by means of the root, which is the first part of the embryo to appear, in preparation for the elongation of the epicotyledonary portion of the shoot, and there is infinite variety in the details of the process.
In albuminous Monocotyledons the cotyledon itself, probably in consequence of its terminal position, is commonly the agent by which the embryo is thrust out of the seed, and it may function solely as a feeder, its extremity developing as a sucker through which the endosperm is absorbed, or it may become the first green organ, the terminal sucker dropping off with the seed-coat when the endosperm is exhausted.
When the cells of the morula stage of an embryo are shaken asunder, each, instead of forming the appropriate part of a single organism, may form a complete new organism.
A slight change in the structure or activity of a gland, by altering the internal secretion, may produce widespread alterations even in an adult organism; and we have good reason to suppose that, if compatible with viability, such minute changes would have even a greater ultimate effect if they occurred in an embryo.
In England, after receiving such modifications - attributed to Burke - as adapted it to the purposes of the opposition, this pamphlet ran through many editions, and procured for its author, as he said, "the honour of having his name inserted in a long list of proscriptions enrolled in a bill of attainder commenced in one of the two houses of parliament, but suppressed in embryo by the hasty course of events."
Symmetrical at their first appearance in the embryo, the somites (from which the myotomes are derived) early undergo a certain distortion, the effect of which is to carry the somites of the left side forwards through the length of one half-segment.
The four principal phases in the development are: (I) Blastula, (2) Gastrula, (3) Flagellate Embryo, (4) Larva.
The embryo now consists of two layers of cells, epiblast and hypoblast, surrounding a cavity, the archenteron, which opens to the exterior by the orifice of invagination or blastopore.
After invagination is completed, the embryo begins to elongate, the blastopore becomes narrower, and the dorsal wall of the gastrula loses its convexity, and becomes flattened to form the dorsal plate, the outer layer of which is the primordium of the neurochord and the inner layer the primordium of the notochord.
About the eighth hour after commencement of development the membrane ruptures and the oval embryo escapes, swimming by means of its flagella at the surface of the sea for another twenty-four hours, during which the principal organs are laid down, although the mouth does not open until the close of this period.
- Diagram of embryo of Amphioxus seen from above in optical section.
(Adapted from Hatschek.) pc, Praechordal head-cavity of embryo; cc, collar-cavity (first somite); my, mesodermic somites (myocoelomic or archenteric pouches); ch, notochord with the neural tube (neurochord) lying upon it; np, anterior neuropore; ne, position of posterior neurenteric canal.
In this genus alone of the known Sympoda the eyes sometimes form a pair, in accordance with the custom of all other malacostracan orders except this and of this order itself in the embryo (Sars, 1900).
Brown's views as to the structure of the unimpregnated ovule (with the introduction of the term "sac embryonnaire"); and in that it shows how nearly Brongniart anticipated Amici's subsequent (1846) discovery of the entrance of the pollen-tube into the micropyle, fertilizing the female cell which then develops into the embryo.
The soul at first is void of content; in the embryo it has not developed beyond the nutritive principle of a plant (Outs): at birth the " ruling part " is a blank tablet, although ready prepared to receive writing.
Cleavage leads to the formation of an epibolic gastrula and ciliated embryo which hatches as a free-swimming larva remarkably like that of a Polychaete worm (D).
AXILE, or Axial, a term (= related to the axis) used technically in science; in botany an embryo is called axile when it has the same direction as the axis of the seed.
The position of the embryo is plainly visible on the front side at the base of the grain.
The testa is thin and membranous but occasionally coloured, and the embryo small, the great bulk of the seed being occupied by the hard farinaceous endosperm (albumen) on which the nutritive value of the grain depends.
The embryo presents many points of interest.
1, back, and 2, front view; 3, vertical section, showing (b) the endosperm, and (a) embryo; 4, beginning of germination, showing (b) the pileole and (c) the radicle and secondary rootlets surrounded by their coleorrhizae.
The scutellum meanwhile feeds the developing embryo from the endosperm.
The persistent bracts (glume and pale) afford an additional protection to the fruit; they protect the embryo, which is near the surface, from too rapid wetting and, when once soaked, from drying up again.
best distinctions are found in the position of the embryo in relation to the endosperm - lateral in grasses, basal in Cyperaceae - and in the possession by Gramineae of the 2-nerved palea below each flower.
Seeds albuminous, with one integument; the single embryo, usually bearing two partially fused cotyledons, is attached to a long tangled suspensor.
After fertilization the ovum-nucleus divides and cell-formation proceeds rapidly, especially in the lower part of the ovum, in which the cotyledon and axis of the embryo are differentiated; the long, tangled suspensor of the cycadean embryo is not found in Ginkgo.
The structure of the seed, the presence of two neck-cells in the archegonia, the late development of the embryo, the partially-fused cotyledons and certain anatomical characters, are features common to Ginkgo and the cycads.
In the Abietineae the cells of the middle tier elongate and push the lowest tier deeper into the endosperm; the cells of the bottom tier may remain in lateral contact and produce together one embryo, or they may separate (Pinus, Juniperus, &c.) and form four potential embryos.
The ripe albuminous seed contains a single embryo with two or more cotyledons.
In Ephedra helvetica, as described by Jaccard, no proembryo or suspensor is formed; but the most vigorous fertilized egg, after undergoing several divisions, becomes attached to a tissue, termed the columella, which serves the purpose of a primary suspensor; the columella appears to be formed by the lignification of certain cells in the central region of the embryo-sac. At a later stage some of the cells in the upper (micropylar) end of the embryo divide and undergo considerable elongation, serving the purpose of a secondary suspensor.
17, B and C, F), and the lower part, which serves only as food-reservoir for the growing embryo, may be termed the sterile half (fig.
One embryo only comes to maturity.
The embryo of Gnetum forms an out-growth from the hypocotyl, which serves as a feeder and draws nourishment from the prothallus.
Soc. (1906) (with bibliography); Lawson, " Sequoia sempervirens," Annals of Botany (1904); Robertson, " Torreya Californica," New Phytologist (1904); Coker, " Gametophyte and Embryo of Taxodium," Bot.
A ring-shaped plate of calcite, secreted by the ectoderm, is then formed, lying between the embryo and the surface of attachment.
The support that appeared to be given to the theory by the presence of supposed calycinal plates in the embryo of echinoids and asteroids has been, in the opinion of many, undermined by E.
6) which, it is supposed, gave rise to the Echinoderma, we infer from embryo FIG.
The early segmentation of the embryo differs in the several groups, but usually the first leaf or leaves, the apex of the stem and the first root are differentiated early, while a special absorbent organ (the foot) maintains for some time the physiological connexion between the sporophyte and the prothallus.
The half of the embryo directed towards the archegonial neck gives rise to the apex of the stem and a sheath of three leaves, the, other half to the small foot and the primary root.
The embryo in L.
This fact leads to the consideration of Phylloglossum, which resembles the embryo of Lycopodium cernuum in so many respects that it has been spoken of as a permanently embryonic form of Lycopod: it is in some respects the simplest existing Pteridophyte.
After fertilization the embryo forms a short suspensor; the apex of the stem, with a leaf on each side of it, is first distinguishable; at the base of this is the foot; while the root arises on the farther side of the latter.
Important points of difference are found in the multiciliate spermatozoids, and in the embryo, which has no suspensor.
In Peripatus the prostomium of the Chaetopod-like ancestor is atrophied, but it is possible that two processes on the front of the head (FP) represent in the embryo the dwindled prostomial tentacles.
study of sections of the embryo m, Mouth.
The two prosthomeres are indicated by their coelomic cavities in the embryo (I and II, fig.
The three prosthomeres or prae-oral somites of Crustacea due to the sinking back of the mouth one somite farther than in Arachnida are not clearly indicated by coelomic cavities in the embryo, but their existence is clearly established by the development and position of the appendages and by the neuromeres.
Three neuromeresa proto-, deutero-, and trito-cerebrum - corresponding to those three prosthomeres are sharply marked in the embryo.
It appears from observation of the embryo that whilst the first prosthomere of Centipedes has its appendages reduced and represented only by eye-patches (as in Arachnida, Crustacea and Hexapoda), the second has a rudimentary antenna, which disappears, whilst the third carries the permanent antennae, which accordingly correspond to the second antennae of Crustacea, and are absent in Hexapoda.
The somites of the abdomen all may carry rudimentary appendages in the embryo, and some of the hinder somites may retain their appendages in a modified form in adult life.
Lankester, " Primitive Cell-layers of the Embryo," Annals and Mag.
minoids may be gained D, Embryo cut through the middle, by simply inspecting the root-end pointing downwards.
The seeds contain a large embryo and no endosperm.
The embryo has now lost its spiral curvature, and becomes completely doubled upon itself, the hind end being in contact with the mouth (fig.
E, side view of later embryo.
F, Ventral view of head of embryo, intermediate between E and G.
G, side view of older embryo.
C, Ventral view of embryo with three pairs of mesoblastic somites, dumb-bell shaped blastopore and primitive s t r e a k.
D, Ventral view of embryo, in which the blastopore has completely closed in its middle portion.
For an account of the further development of the megaspore, and the formation of the egg-cell, from which after fertilization is formed the embryo, see Gymnosperms and Angiosperms.
Consequent upon this, after a longer or shorter period, those changes commence in the embryo-sac which result in the formation of the embryo plant, the ovule also undergoing changes which convert it into the seed, and fit it for a protective covering, and a store of nutriment for the embryo.
The vegetable oils and fats occur chiefly in the seeds, where they are stored to nourish the embryo, whereas in animals the oils and fats are enclosed mainly in the cellular tissues of the intestines and of the back.
It is a curious fact that in no case has an embryo been found in any of these seeds; probably fertilization took place after they were shed, and was followed immediately by germination.
I I, Bennettites seed in longitudinal section, showing the dicotyledonous embryo; p, cotyledons; r, radicle; s, testa.
Development and Metamorphosis.-In a great number of batrachians, including most of the European species, the egg is small and the food-yolk is in insufficient quantity to form an external appendage of the embryo.
It was suggested that universal abhorrence at experimentation would be felt if the embryo was regarded as " human " .
Front and back At six days old, the embryo, now called a blastocyst, consists of only a few hundred cells.
blastocyst mouse embryo, single cells can contribute to most, if not all somatic cell types.
blastula stage Xenopus embryo showing multiple, synchronously dividing cells.
blighted ovum mean there was no embryo?
brine shrimp embryo also requires less energy to break through a hatching membrane than a thick outer shell.
button-down collars and leather caps are all would-be Beatles or embryo Donovans.
He compares the tube heart of an embryo to that of the primitive chordate, Amphioxus.
He supports the use of the human embryo for experiments and the production of the embryonic human clone for the same purpose.
Expansion of the extra-embryonic coelom cavity allows the yolk sac and allantois to expand into the coelom cavity allows the yolk sac and allantois to expand into the coelom cavity from the gut of the embryo.
commune called Embryo in places such as Afghanistan, Nepal and Pakistan.
PCR (polymerase chain reaction) is used to detect a single.g.ne disorder e.g. cystic fibrosis in an embryo.
The " Folders " section covers a number of bioethical topics, including embryo research, stem cells, cloning, and pre-implantation diagnosis.
Tides have a vital role to play in the formation of embryo dunes, by depositing tidal litter.
The first cells of this sort to form in the embryo are called the ectoderm, the mesoderm and the endoderm.
ectoderm layer in the embryo.
A cloned human embryo is created in both cases.
MAP may also disrupt implantation or cause the loss of a newly implanted embryo.
embryo implantation was unsuccessful and the couple then separated.
embryo experimentation and euthanasia.
embryo splitting was first used to produce genetically identical sheep ten years ago at Cambridge.
embryo dunes build up, the sand supply to existing dunes is cut off and they become more subject to visitor damage.
Embryo biopsy: The removal and culture of one or two cells from an embryo biopsy: The removal and culture of one or two cells from an embryo in vitro prior to genetic screening.
Proteins in the growing ridge (dark band) of a limb bud in a chick embryo.
The rats will be humanely killed to supply serum, which is essential for the in vitro culture of mouse embryo tissues.
embryo before implantation.
embryo in vitro.
It is possible to remove cells from early pre-implantation embryos without damage to the original embryo.
envisage the scenario where the only successful nuclear transfers were from a single original embryo.
Even the Warnock Committee had a minority report which regarded the human embryo as unsuitable for destructive experimentation.
Thus abortion, the " morning after " pill and embryo experimentation remain illegal, but the " x " case exception still stands.
Budding of Rous sarcoma virus and vesicular stomatitis virus from localized lipid regions in the plasma membrane of chicken embryo fibroblasts.
But surprisingly, mice embryo fibroblasts (MEFs) derived from these embryos proliferated normally and ERK activation was also completely normal.
Any amount for a mare's unborn foal, embryo or fetus.
In flowering plants, anther s produce pollen which contains male gametes, and the embryo sac within the ovary contains a female gamete.
The embryo has also been subject to linguistic gymnastics.
You consider the Gnostic heresy that is here in embryo in this book.
Embryo research will always remain morally impermissible for a large section of the population.
The early embryo is not in able to make informed consent in plans concerning its own future.
isolated from an embryo or adult tissue, or allowed to differentiate from the resulting stem cells.
Further developments in DNA technology now allow technicians to determine a pre- implantation embryo ' s histocompatibility leukocyte antigen (HLA ).
magician's wand is an embryo scepter, and historical kings still retain many trappings from their magic office.
Pregnancies and deliveries after in vitro maturation culture followed by in vitro fertilization and embryo transfer without stimulation in women with polycystic ovary syndrome.
mesoderm forms in the equatorial region of the embryo, a result of signals generated by neighboring endodermal cells (1 ).
Mr Paul Szabo MP has called for an indefinite moratorium on embryo research.
mouse embryo tissues.
A tiny embryo is aware, even before the central nervous system is formed.
Just like a leech derives nourishment from its host's blood, the embryo derives nourishment from the decidua or the pregnant endometrium.
Sunday Post Quiz Answers, June 8, 2003 1 To provide nourishment for the bird or animal embryo.
A cloned embryo is created by cell nuclear transfer from an adult cell into an enucleated oocyte.
oocyte recovery and embryo transfer techniques for IVF 15.
It was unfortunate that the definition of an embryo in the HFEA overlooked that cloning could be done using an unfertilised ovum.
Human cloning produces an embryo by fusing the nucleus of a body cell with an enucleated ovum.
ovumrtilized human ova grown in vitro to the early embryo stage can be selected for implantation.
perplexing question has been raised about the status of the embryo in relation to identical twins.
protoplast fusion, embryo rescue and assisted pollination, double haploid breeding, genomics, proteomics and genetic modification.
The initial segmentation of the embryo is dependent upon concentration biases in the fertilized egg.
The brine shrimp embryo also requires less energy to break through a hatching membrane than a thick outer shell.
Mr Slope, great as he was with embryo grandeur, still came to see the signora.
The HFEA will not license research projects involving embryo splitting with the intention of increasing the number of embryos for transfer.
These procedures are utilized in somatic cell nuclear transfer (SCNT ), a type of embryo stem cell research, and in IVF.
test tubethe lamb born from the test-tube embryo, is an identical twin of the " parent " ewe that donated the cell.
thermometer readings will not be the same as embryo temperatures when cooling or heating occurs.
unborn foal, embryo or fetus.
Excess non-protein nitrogen in the form of dietary urea reduced embryo quality.
One of the sperm fuses with egg to form a single cell called a zygote, which then starts dividing and becomes an embryo.
The fruit is berry-like, and the seeds are remarkable for having their embryo surrounded by an endosperm as well as by a perisperm.
The vast majority of the mammalia are provided with an organ in the uterus, by which, before the birth of their young, a vascular connexion is maintained between the embryo and the parent animal.
(2) To the second class belong Ankylostoma, Strongylus and many species of Ascaris; the embryo on leaving the egg lives free in water or damp earth, and resembles very closely the free-living genus Rhabditis.
This theory of Brahma being born from a golden egg is, however, a mere adaptation of the Vedic conception of Hiranya-garbha (" golden embryo"), who is represented as the supreme god in a hymn of the tenth (and last) book of the Rigveda.
There is no free-swimming planula larva, but the stage corresponding to it is passed over in an enveloping cyst, which is secreted round the embryo by its own ectodermal layer, shortly after the germ-layer formation is complete, i.e.
Protected by the double envelope, the embryo is set free as a so-called " egg," and in Europe it passes the winter in this condition.
In the spring the embryo bursts its shell and is set free as a minute actinula which becomes a Hydra.
During the process of fertilization in the Angiosperms it has been shown by the researches of Nawaschin and Guignard that in Lilium and Fritillaria both generative nuclei enter the embryo sac, one fusing with the oosphere nucleus, the other with the polar nuclei (fig.
Both nuclei are elongated vermiform structures, and as they enter the embryo sac present a twisted appearance like a spermatozoid without cilia (fig.
The embryo is generally surrounded by a larger or smaller amount of foodstuff (endosperm) which serves to nourish it in its development to form a seedling when the seed germinates; frequently, however, as in pea or bean and their allies, the whole of the nourishment for future use is stored up in the cotyledons themselves, which then become thick and fleshy.
Protected between the cotyledons and terminating the axis of the plant is the first stem-bud (the plumule of the embryo), by the further growth and development of which the aerial portion of the plant, consisting of stem, leaves and branches, is formed, while the development of the radicle forms the root-system.
Vezhdovsky to exist in the embryo of certain forms. The blood in the Chaetopoda consists of a plasma in which float a few corpuscles.
It has been shown (Bourne) that the "perichaetous" condition is probably secondary, inasmuch as in worms which are, when adult, "perichaetous" the setae develop in pairs so that the embryo passes through a stage in which it has four bundles of setae, two to each bundle, the prevalent condition in the group. Rarely there is an irregular disposition of the setae which are not paired, though the total number is eight to a segment (fig.
But in these epibolic forms, just as in the embolic Paludina, the embryo proceeds to develop its ciliated band and shellgland, passing through the earlier condition of a trochosphere to that of the veliger.
In Limnaeus the permanent shell is preceded in the embryo by a wellmarked shell-gland or primitive shell-sac (fig.
m, Mouth; f, foot; v, velar area, the margin v corresponding with the ciliated band which demarcates the velar area or velum of the embryo Gastropod (see fig.
60 represents such an embryo under slight compression as seen by transmitted light.
- Among the Hexapoda, as in Arthropods generally, the egg is large, containing an accumulation of yolk for the nourishment of the growing embryo.
- The embryo begins to develop as an elongate, thickened, ventral region of the blastoderm which is known as the ventral plate or germ band.
stated that in the Muscidae, while the anterior endoderm-rudiment The embryo is invaginated into the yolk, but the surface edges of arises as Kowalevsky had observed, the posterior part of the " midthe blastoderm do not close over, so that a groove or pore puts gut " has its origin as a direct outgrowth from the proctodaeum.
On this view Wheeler, however, compares with the " dorsal organ " the peculiar the entire food-canal in most Hexapoda must be regarded as of extra embryonic membrane or indusium which he has observed ectodermal origin, the " endoblast " represents mesoderm only, between serosa and amnion in the embryo of the grasshopper and the median furrow whence it arises can be no longer compared Xiphidium.
- The segments are perceptible at a very regarded as the true endoderm in the hexapod embryo, for he states early stage of the development as a number of transverse bands (1897) that in the bristle-tail Lepisma and in dragon-flies they give arranged in a linear sequence.
The other is the segment of the maxillulae (see above, under Jaws), behind the mandibular somite; the presence of this in the embryo of the collembolan Anurida has been lately shown (1900) by J.
Folsom has detected in the embryo of Anurida a pair of ganglia (fig.
The mass of cells undergoes segmentation corresponding with the outer segmentation of the embryo, and a pair of cavities - the coelomic pouches (fig.
In the embryo Limulus (fig.
But in 1896 Dr August Brauer of Marburg (9) discovered in the embryo of Scorpio a seventh prosomatic somite (see VII PrG, figs.
- The prae-genital somite fuses in the embryo with the prosoma and disappears (see fig.
One view, the monozoic, regards the whole development as a prolonged metamorphosis; another, the polyzoic view, considers that not only is the Cestode a colony, the proglottides being produced asexually, but that the scolex which buds off these individuals is itself a bud produced by the spherical embryo or onchosphere.
The result of this process is a minute ovoid embryo consisting of a solid mass of cells surrounded by a follicle of flattened yolk-cells.
c, Nearly ripe cercariae; cc, cystogenous cells; dr, daughter-redia; dt, limbs of the digestive tract; f, head-papilla; h, eye-spots; h', same degenerating; k', germinal cell; 1, cells of the anterior row; m, embryo in optical section, gastrula stage; n, pharynx of redia; o, digestive sac; oe, oesophagus.
On the news of the battle (coupled with that of a fresh army appearing on the Korean coast),' Kuropatkin instantly sent off part of his embryo central mass to bar the mountain passes of Fenshuiling and Motienling against the imagined relentless pursuit of the victors, and prepared to shift his centre of concentration back to Mukden.
The formation of an inner cell-mass converts the singlelayered blastula (monoblastula) into a double-layered embryo (diblastula) which may be termed a parenchymula, since at first the inner cell-mass forms an irregular parenchyma which may entirely fill up and obliterate the segmentation cavity (fig.
- Embryo of Pisid- fertilized, and advance whilst still in ium pusillum in the diblastula this position to the glochidium phase stage, surface view (after Lanof development (fig.
In some plants the nucellus is not thus absorbed, but itself becomes a seat of deposit of reserve-food constituting the perisperm which may coexist with endosperm, as in the water-lily order, or may alone form a food-reserve for the embryo, as in Canna.
The embryo is set free as a planula larva (fig.
Three must be considered: (I) the scutellum, connected by vascular tissue with the vascular cylinder of the main axis of the embryo which it more or less envelops; it never leaves the seed, serving merely to prepare and absorb the food-stuff in the endosperm; (2) the cellular outgrowth of the axis, the epiblast, small and inconspicuous as in wheat, or larger as in Stipa; (3) the pileole or germ-sheath, arising on the same side of the axis and above the scutellum, enveloping the plumule in the seed and appearing above ground as a generally colourless sheath from the apex of which the plumule ultimately breaks (fig.
The radicle then breaks through the coleorhiza, as do also the secondary rootlets where, as in the case of many cereals, these have been formed in the embryo, (fig.
Recent investigations (Folsom, 4) show the existence in the embryo of a prae-maxillary or supra-lingual somite which is suppressed during development.
On quitting the shelter of the parent tentacles the embryo becomes a pelagic larva, known as Actinotrocha (fig.
The elongation of the embryo is accompanied by an elongation of the blastopore, which soon becomes dumb-bell shaped (fig.
The seeds have in some cases been preserved in wonderful perfection, enabling one to make out the structure of the embryo, with its bluntly conical radicle and two fleshy cotyledons filling the exalbuminous seed (fig.
Allowing embryo research in the UK to include the investigation of regenerative cell therapies will pave the way for treatments for hitherto incurable diseases.
By the sixth week of pregnancy the embryo is already encased in an amniotic sac of fluid.
These procedures are utilized in somatic cell nuclear transfer (SCNT), a type of embryo stem cell research, and in IVF.
Dolly, the lamb born from the test-tube embryo, is an identical twin of the " parent " ewe that donated the cell.
Remember that incubator thermometer readings will not be the same as embryo temperatures when cooling or heating occurs.
Nevertheless, some mice will be operated on during the embryo transfer and vasectomy procedures but these operations will be performed under general anesthesia.
I saw the face of an embryo with large, wide-open eyes.
All the nutrients required for embryo development are already present within the fertilized egg, stored in the form of yolk protein molecules.
The most likely explanation for this phenomenon is that a cat with two faces is actually the result of a protein that disrupts embryo development.
Identical twins represent the splitting of a single fertilized zygote (union of two gametes or male/female sex cells to produce a developing embryo) into two separate individuals.
Their use is controversial because such stem cells cannot be used in research without destroying the living embryo.
Teratogen-Any drug, chemical, maternal disease, or exposure that can cause physical or functional defects in an exposed embryo or fetus.
Urogenital-Refers to both the urinary system and the sexual organs, which form together in the developing embryo.
Birth defects can result from the variation in a woman's blood sugar level during the first eight to 12 weeks, which is the time period when the embryo is developing.
Between 10 and 14 weeks of pregnancy, physicians may use an ultrasound to look for a thickness at the nuchal translucency, a pocket of fluid in back of the embryo's neck, which may indicate a cardiac defect in 55 percent of cases.
Nuchal translucency-A pocket of fluid at the back of an embryo's neck, visible via ultrasound.
The neural tube of the embryo develops into the brain, spinal cord, spinal column, and the skull.
Studying prenatal human development is difficult because the embryo and fetus develop in a closed environment-the mother's womb.
Until the end of the eighth week the developing organism is called an embryo.
During the first eight weeks of pregnancy, organogenesis (the formation of organs) is taking place, which places the embryo at a higher risk of deformities when exposed to teratogens.
Miscarriage-Loss of the embryo or fetus and other products of pregnancy before the twentieth week.
In the first stage, four to 20 weeks gestation, rapid cell division and multiplication (hyperplasia) occurs as the embryo grows into a fetus.
Preimplantation genetic diagnosis (PGD) is a relatively new technique that involves in-vitro fertilization followed by genetic testing of one cell from each developing embryo.
Sometimes a child may end up with more than 46 chromosomes because of problems with the father's sperm or the mother's egg or because of mutations that occurred after the sperm and the egg fused to form the embryo (conception).
A condition called trisomy occurs when three, instead of two, copies of a chromosome are present in a developing human embryo.
The most well-known trisomy-related disorder is Down syndrome (trisomy 21), in which the developing embryo has an extra copy of chromosome 21.
Patau syndrome is trisomy 13, in which the developing embryo has three copies of chromosome 13.
Most girls with Turner syndrome do not have ovaries with healthy oocytes capable of fertilization and embryo formation.
Prenatal development refers to the process in which a baby develops from a single cell after conception into an embryo and later a fetus.
As the embryo develops, each germ layer differentiates into different tissues and structures.
The embryo is now referred to as a fetus.
When an embryo becomes a fetus at eight weeks, it is approximately 3 centimeters (1.2 inches) in length from crown to rump and weighs about 3 grams (0.1 ounce).
The age, health status, nutritional status, and environment of the mother are all closely tied to the health of a growing embryo or fetus.
Birth Defects Research Part C: Embryo Today: Reviews 69 (2003): 286-304.
Purified chick embryo cell (PCEC) vaccine became available in the United States in 1997.
Purified chicken embryo cell vaccine (PCEC)-A rabies vaccine in which the virus is grown in cultures of chicken embryo cells, inactivated, and purified for IM injection.
Iodine is needed to make thyroid hormone, which has a variety of roles in human embryo development.
Congenital brain defects may be caused by inherited genetic defects, spontaneous mutations within the genes of the embryo, or effects on the embryo due to the mother's infection, trauma, or drug use.
An autosomal dominant form of VWD can be inherited from either parent or can occur as a spontaneous gene mutation (change) in the embryo that is formed when the egg and sperm cells come together during fertilization.
By the end of the fifth week, the embryo has doubled in size and has grown a tail-like structure that becomes the coccyx (lowermost tip of the backbone).
By the seventh week the embryo is about 2 cm (1 in) long and facial features are visible.
Androgens regulate the development of the embryo, determining whether it is a male or a female (male in the presence of androgens and female in the absence of androgens).
Female is the default sex of the embryo, so most of the sex organ deficits at birth occur in boys.
The error that causes the extra Y chromosome can occur in the fertilizing sperm or in the developing embryo.