Serially homologous structures, borne on the same body, are commonly differ s entiated into sets, the mean character of a set produced in one part of the body, or during one period of life, differing from the mean character of a set produced in a different region or at a different time.
By Haeckel they are considered homologous with the umbrella of a medusa.
Homologous structures were such as, though greatly differing in appearance and detail from one another, and though performing widely different functions, yet were capable of being shown by adequate study of a series of intermediate forms to be derived from one and the same part or organ of the " plan-form " or " archetype."
Considering the predicted series of compounds C7,H2,,+2, which is the well-known homologous series of methane, the first member, the possible of isomerism lies in that of a different linking of the carbon atoms. This first presents itself when four are present, i.e.
Experience has shown that such mono-derivatives as nitro compounds, sulphonic acids, carboxylic acids, aldehydes, and ketones yield as a general rule chiefly the meta-compounds, and this is independent of the nature of the second group introduced; on the other hand, benzene haloids, amino-, homologous-, and hydroxy-benzenes yield principally a mixture of the orthoand para-compounds.
Heterocyclic rings may be systematically surveyed from two aspects: (I) by arranging the rings with similar hetero-atoms according to the increasing number of carbon atoms, the so-called " homologous series "; or (2) by first dividing the ring systems according to the number of members constituting the ring, and then classifying these groups according to the nature of the hetero-atoms, the so-called " isologous series."
Recent researches have shown that the law originally proposed by Kopp - " That the specific volume of a liquid compound (molecular volume) at its boiling-point is equal to the sum of the specific volumes of its constituents (atomic volumes), and that every element has a definite atomic value in its compounds " - is by no means exact, for isomers have different specific volumes, and the volume for an increment of CH 2 in different homologous series is by no means constant; for example, the difference among the esters of the fatty acids is about 57, whereas for the aliphatic aldehydes it is 49.
185.8° Equal increments in the molecule are associated with an equal rise in the boiling-point, but this increment varies in different homologous series.
While certain additive relations hold between some homologous series, yet differences occur which must be referred to the constitution of the molecule.
By subtracting the value for CH 2, which may be derived from two substances belonging to the same homologous series, from the molecular refraction of methane, CH 4, the value of hydrogen is obtained; subtracting this from CH 2, the value of carbon is determined.
Many instances have been recorded where substitution has effected a deformation in one particular direction, the crystals of homologous compounds often exhibiting the same angles between faces situated in certain zones.
His homologous structures are now spoken of as " homogenetic " structures, the idea of community of representation in an archetype giving place to community of derivation from a single representative structure present in a common ancestor.
These processes are not altogether homologous with those of the ovipositor, being formed by inner and outer lobes of a pair of structures on the ninth abdominal segment.
The " brush-formed " organs of the Podocopa are medially placed, and, in spite of their sometimes forward situation, Miller believes among other possibilities that they and the penis in the Cypridinidae may be alike remnants of a third pair of legs, not homologous with the penis of other Ostracoda (Podocopa included).
Gruber and Durham showed that sedimentation occurred when a small quantity of the homologous serum was added to an emul:_on of the bacterium in a small test-tube, and found that this obtained in all cases where Pfeiffer's lysogenic action could be demonstrated.
The view is commonly held that these eye-stalks are really limbs, homologous with the other appendages.
This is probably homologous with the hydrom cylinder in the stems of other mosses.
The stereom is furnished either by cortical cells or by the tracheal elements, in a few cases by fibres which arc probably homologous with sievetubes.
The midbrain is represented chiefly by the optic lobes, the cortex of which alone is homologous with the corpora quadragemina of the mammals.
16), extending between the fenestra ovalis and the tympanic membrane or drum, consists of (I) the long and slen der columella, a straight, ossified rod which fits with a disk into the fenestra r; t st ovalis; it is homologous with the stapes (m.st.), although not stirrupshaped; (2) the extra-columellar mass.
This long downward process being homologous with an almost exactly identical arrangeFIG.
This organ is probably homologous with the byssogenous gland of Lamellibranchs.
These he considered to be homologous with the arms of Cephalopods.
The fins of Pteropods are now interpreted as the expanded lateral margins of the foot, termed parapodia, not homologous with the siphonof Cephalopods which is formed from epipodia.
Soc., 18 93, 6 3, p. 465) states, that the melting-point of any odd member of a homologous series is lower than the melting-point of the even member containing one carbon atom less.
At a temperature of about 300-400° C. the alkyl chloride formed in this reaction attacks the benzene nucleus and replaces hydrogen by an alkyl group or groups, forming primary amines homologous with the original amine; thus methylaniline hydrochloride is converted into paraand ortho-toluidine hydrochloride, and trimethyl phenyl ammonium iodide is converted into mesidine hydriodide.
Later still he engaged in the study of the relations between chemical constitution and rotation of the plane of polarization in a magnetic field, and enunciated a law expressing the variation of such rotation in bodies belonging to homologous series.
In most rotifers, on the contrary, the trochus is stronger than the cingulum, often lobed, and with some of its cilia aggregated into vibratile styles homologous with the combplates of Ctenophora (q.v.) and the membranelles of ciliate Infusoria (q.v.).
In all other Trypanosomes there is only one flagellum, which is invariably attached to the body in the same manner as the posterior one of biflagellate forms. This flagellum, however, is most probably not to be considered homologous in all cases.
This byssus is not homologous with that of other Lamellibranchs, but originates from a single glandular epithelial cell embedded in the tissues on the dorsal anterior side of the adductor muscle.
The investigation also showed that the nature of the acid used affected the result, for in an homologous series of acids it was found that as the molecule of the acid became more complex, the rate of esterification became less.
It may be remarked that since this line joins homologous points of two similar rows it will envelope a parabola.
Pyocyaneus that when a small quantity of the homologous serum (i.e.
At the same time it is necessary to observe that it is by no means certain that the mesoderm found in various groups of Metazoa is a similar or homologous formation in all cases.
Each taeniola bears a strongly developed longitudinal muscle-band, stated by Claus and Chun to be developed from the endoderm, like the retractor muscles of the anthopolyp, but by other investigators it is affirmed that each retractor muscle of the scyphistoma arises from the lining of a funnel-shaped ectodermal ingrowth (" Septaltrichter ") growing down from the peristome inside each taeniola, in a manner similar to the infundibular cavities of Lucernaria, which in their turn are homologous with the sub f genital cavities of Scypho l A .` medusae.
Each ovule is enclosed at the base by an envelope or collar homologous with the lamina of a leaf; the fleshy and hard coats of the nucellus constitute a single integument.
An opening to the exterior S From a comparison of the two embryological types there can be no doubt on two points; first, that the pneumatophore and the protocodon are strictly homologous, and, therefore if the nectocalyx is comparable to the umbrella of a medusa, as seems obvious, the pneumatophore must be so too; secondly, that the coenosarcal axis arises from the ex-umbrella of the medusa and cannot be compared to a manubrium, but is strictly comparable to the " bud-spike " of a Narcomedusan.
The leaves of the true mosses and those of the club-mosses (Lycopodium, Selaginella) being somewhat alike in general appearance and in ontogeny, might be, and indeed have been, regarded as homologous on that ground.
For instance, all the leaves of the Bryophyta are generally homologous inasmuch as they are all developments of the gametophyte.
All organs performing the same function and showing similar adaptations are said to be analogous or homoplastic, whatever their morphological nature may be; hence organs are sometimes both homologous and analogous, sometimes only analogous.
The tendrils of a vetch and of a cucumber are analogous, and also homologous because they both belong to the category leaf; but they are only analogous to the tendrils of the vine and of the passion-flower, which belong to the category stem.
Later on fused with, a pair of membrane bones, the basi-temporals, homologous in part with the parasphenoid of lower vertebrates.
It is homologous with the distal ends of the ceratohyals or ventral elements of the hyoidean or second visceral arch.
The pubis consists of a short anterior portion (spina pubica or pectineai process, homologous with the prepubic process of Dinosaurs) and the long and slender pubis proper (equivalent to the processus lateralis pubis of most reptiles).
This great muscle covers completely the supracoracoideus, generally described as the second pectoral, or subclavius muscle, in reality homologous with the mammalian supraspinatus muscle.
It therefore appears that the difference between the heats of combustion of two adjacent members of a series of homologous compounds is practically a constant, and that this constant has two average values, viz.
The mere retention of the same crystal form by homologous substances is not a sufficient reason for denying a morphotropic effect to the substituent group; for, in the case of certain substances crystallizing in the cubic system, although the crystal form remains unaltered, yet the structures vary.
There is thus a minimum circulation in the greater depths causing there uniformity of temperature, an absence of the circulation of oxygen by other means than diffusion, and a protection of the sulphuretted hydrogen from the oxidation which takes place in homologous situations in the open ocean.
If, in the extensive calculus of the nth category, all the units (including i and the derived units E) are taken to be homologous instead of being distributed into species, we may regard it as a (2'-I)-tuple linear algebra, which, however, is not wholly associative.
In such examples as the above we may regard the hymenium (Solenia, Cyphella), zygospores, or asci as truly invested by later growth, but in the vast majority of cases the processes which result in the enclosure of the spores, asci, &c., in a "fructification" are much more involved, inasmuch as the latter is developed in the interior of hyphal tissues, which are by no means obviously homologous with a stroma.
These mountain systems are homologous in structure with those, not of Celebes or of Halmahera, but of Malacca, Banka and Billiton.
3, T), has been much discussed, some authorities holding that it is a true somite, homologous with those which precede it.
The fact that in certain rare cases among insects a leg may apparently be replaced by a wing tends to show that under exceptional conditions similar forms may be assumed by non-homologous parts.
The morphology of the female flowers has been variously interpreted by botanists; the peduncle bearing the ovules has been described as homologous with the petiole of a foliage-leaf and as a shoot-structure, the collar-like envelope at the base of the ovules being referred to as a second integument or arillus, or as the representative of a carpel.
(4) A pair of thyrohyals, homologous with the posterior hyoid horns of mammals, i.e.
Serially homologous with the intervertebral pads.
The development of the armature has been little studied, and the question whether there may be present gonapophyses homologous with those of the female is open.
All members that belong to the same category are sitting together.