The irritation set up by the hatching egg and its resulting larva appears to be the stimulus to development, and net a poison or enzyme injected by the insect.
A full-grown larva digs a pit about 2 in.
The beetles are fierce Antenna of Larva of Gyrinus.
The carabid larva is an active well-armoured grub with the legs and cerci variable in length.
The larva pierces the vessels of the plant with sharp processes at the hinder end of its body.
extremes we find various transitional forms: an active larva, as described above, but with four-segmented, single-clawed legs, as among the rove-beetles and their allies; the body well armoured, but slender and worm-like, with very short legs as in wireworms and mealworms (figs.
Larva, or mealworm.
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.
a, Beetle; b, head of beetle with feelers and palps; c, larva; d, pupa.
The most striking feature in the development of beetles is the great diversity noticeable in the outward form of the larva in different families.
without a hydroid phase; the medusa develops directly from the actinula larva, which may, however, multiply by budding.
With very few exceptions, the larva in this group is active and campodeiform, with cerci and elongate legs as in the Adephaga, but the leg has only four segments and one claw.
2, C): the larva therefore resembles Nautilus in the relations of body and shell.
Riley, who finds that the young larva, hatched from the egg laid on the pod, has three pairs of legs, and that these are lost after the moult that occurs when the grub has bored its way into 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.
a, Male; b, female; c, larva (ventral view).
The larva has a breathing-tube, and floats head downwards; when disturbed it wriggles to the bottom (Christy).
The chief modifications of this form are seen in the Mitraria larva of Ammochares with only the preoral band, which is much folded and which has provisional and long setae; the a.trochous larva, where the covering of cilia is uniform and not split into bands; and the polytrochous larva where there are several bands surrounding the body.
The pallial cavity, with its organs, is by this torsion moved up the right side of the larva to the dorsal surface, and thus the left organs become right and vice versa.
In those Euthyneura in which the shell is entirely absent in the adult, it is, except in the three genera Cenia, Runcina and Vaginula, developed in the larva and then falls off.
The worm inhabits the lung of the frog and toad, and is hermaphrodite (Schneider) or parthenogenetic (Leuckart); the embryos hatched from the eggs find their way through the lungs into the alimentary canal and thence to the exterior; in a few days they develop into a sexual larva, called a Rhabditiform larva, in which the sexes are distinct; the eggs remain within the uterus, and the young when hatched break through its walls and live free in the perivisceral cavity of the mother, devouring the organs of the body until only the outer cuticle is left; this eventually breaks and sets free the young, which are without teeth, and have therefore lost the typical Rhabditis form.
The reproductive organs do not begin to appear until the larva has twice cast its skin.
When the latter is reached and the pit completed, the larva settles down at the bottom, buried in the soil with only the jaws projecting above the surface.
Clinging to her hairs they are carried to the nest, where they bore into the body of a bee or wasp larva, and after a moult become soft-skinned legless maggots.
One species, the slugworm (Eriocampa liynacina), is common to Europe and America; the larva is a curious slug-like creature, found on the upper surface of the leaves of the pear and cherry, which secretes a slimy coating from its skin.
The larva makes a globular case of .sand stuck together with fine silk spun, it is said, from a slender spinneret at the posterior end of the body.
Similarly the newly-hatched larva of an oil-beetle (Meloe) is an active little campodeiform insect, which, hatched from an egg laid among plants, waits to attach itself to a passing bee.
Sharp; in the stag-beetle larva a series of short tubercles on the hind-leg is drawn across the serrate edge of a plate on the haunch of the intermediate legs, while in the Passalid grub the modified tip of the hind-leg acts as a scraper, being so shortened that it is useless for locomotion, but highly specialized for producing sound.
The growth of the parasitic larva does not stop the development of the host-larva, and when the latter pupates and assumes the winged form, the stylopid, which has completed its transformation, is carried to the outer world.
The most active form of larva found in this family resembles in shape that of a ladybird, tapering towards the tail end, and having the trunk segments protected by small firm sclerites.
- A, Side view of the larva of Lopadorhynchus (from Kleinenberg), showing the developing trunk region.
A tadpole is the larva of a tailless Batrachian after the loss of the external gills and before the egress of the fore limbs (except in the aberrant Xenopus) and the resorption of the tail.
Larva of Dyticus Cybister sp. (Water-Beetle).
a, Calandra granaria; b, larva; c, pupa; d, C. oryzae.
The generalized arrangement of the wing-nervure and the nature of the larva, which is less unlike the adult than in other beetles, distinguish this tribe as primitive, although the perfect insects are, in the more dominant families, distinctly specialized.
The "` bacon beetle" (Dermestes lardarius), and its hard hairy larva, are well known.
The first larval stage is the "triungulin," a tiny, active, armoured larva with long legs (each foot with three claws) and cercopods.
After eating the contents of the egg, the larva moults and becomes a fleshy grub with short legs and with paired spiracles close to the dorsal region, so that, as it floats in and devours the honey, it obtains a supply of air.
In the American Epicauta vittata the larva is parasitic on the eggs and eggcases of a locust.
There it feeds first as an internal parasite of the waspgrub, then bores its way out, moults and devours the wasp larva from outside.
Among the vegetable-feeding chafers we usually find that while the perfect insect devours leaves, the larva lives underground and feeds on roots.
Mosquitoes go through four phases: (1) ovum, (2) larva, (3) nympha, (4) complete insect.
The larva has no breathing-tube, and floats horizontally at the surface, except when feeding; it does not frequent sewage or foul water.
In these forms the pregnant female, instead of laying eggs, as Diptera usually do, or even producing a number of minute living larvae, gives birth at one time but to a single larva, which is retained within the oviduct of the mother until adult, and assumes the pupal state immediately on extrusion.
a, Female; b, female after loss of wings; c, male; d, worker; e, larva; g, pupa (magnified four times); f, head of larva more highly magnified.
B, Side view of the trochophore larva of Eupomatus uncinatus (from Hatschek).
He referred also to the nautiloid shell of the larva falling to one side.
At the end of this stage, the larva will spin a cocoon.
Monthly preventative heartworm medication kills the larva that entered into the dog's body over the past 30 to 45 days.
Daily medication is only effective in killing any larva that entered the dog's body during the past 24 to 48 hours.
The majority of the flea infestation is made up fleas in various life cycle stages, meaning eggs, larva or the pupa.
From fecund egg to ravenous caterpillar (larva) to metamorphosing pupa to parental adult, the butterfly's life is profoundly meaningful.
The embryo is set free as a planula larva (fig.
The larva after fixation changes into a polyp-like organism termed a scyphistoma or scyphopolyp (fig.
A, Male scale insect; B, female; C, larva; D, female scale; E, male scale.
The perfect frog, after transformation, is smaller than the larva.
the numerous galls on the oakbut the gall itself furnishes well adapted protection and abundant stores of nutriment to its particular larva, and often appears to be borne without injury to the plant.
Slipping to the bottom the prey is immediately seized by the lurking ant-lion; or if it attempt to scramble again up the treacherous walls of the pit, is speedily checked in its efforts and brought down by showers of loose sand which are jerked at it from below by the larva.
The triungulin searches for the eggs, and, after a moult, becomes changed into a soft-skinned tapering larva.
Fabre states that the mother-insect carefully arranges the food-supply so that the most nutritious and easily digested portion is nearest the egg, to form the first meal of the young larva.
14), and the presence of an anterior and posterior sucker, produce a looping mode of progression similar to that of a Geometrid larva.
the nautiloid shell In Planorbis and in Auricula (Pulmonata, formed on the larva allied to Limnaeus) the olfactory organ is being cast, and a new on the left side and receives its nerve from shell of a different form the left visceral:ganglion.
- e,f, Owl moth (Heliothis armigera); a,b, egg, highly magnified; c, larva or caterpillar; d, pupa in earthen cell.
Such a young insect is a larva - a term used by zoologists for young animals generally that are decidedly unlike their parents.
It is obvious that the hatching of the young as a larva necessitates h After Heymons, Zeit.
21, d) is revealed, exhibiting the wings and other imaginal structures, which have been developed unseen beneath the cuticle of the larva.
the ingpositionofimaginalbuds maggots of the blowfly, Calliphora in larva of fly.
I., II., III., vomitories) the imaginal disks are to all the three thoracic segments appearance completely separated from of the larva; I, 2, 3, buds the hypodermis, with which they are, of the legs of the imago; la, however, really organically connected bud of head-lobes; f, of by strings or pedicels.
This type of active, armoured larva - of ten bearing conspicuous feelers on the head and long jointed cercopods on the tenth abdominal segment - was styled campodeiform by F.
25) - a vermiform podeiform Larva of larva, with soft, white, feebly-chitinized a Ground-Beetle cuticle and without either head-capsule (A epus marinus).
- Vermiform Larva (maggot) of House-fly (Musca domestica).
boring grub of a longhorn-beetle or of the saw-fly Sires, with its stumpy vestiges of thoracic legs; the large-headed but entirely legless, fleshy grub of a weevil; and the legless larva, with greatly reduced head, of a bee.
These later stages, comprising the greater part of the larval history, are adapted for an inquiline or a parasitic life, where shelter is assured and food abundant, while the short-lived, active condition enables the newly-hatched insect to make its way to the spot favourable for its future development, clinging, for example, in the case of an oil-beetle's larva, to the hairs of a bee as she flies towards her nest.
- a, Saw-toothed Grain-Beetle (Silvanus surinamensis); b, pupa; c, larva, magnified 12 times; d, feeler of larva.
Larva campodeiform or eruciform.
Orthorrhapha: Larva eruciform.
Cyclorrhapha: Larva vermiform (no head-capsule).
Larva eruciform, limbless.
Larva eruciform, with seven or eight pairs of abdominal prolegs, or entirely legless.
Fragmentary as the records are, they show that the Exopterygota preceded the Endopterygota in the evolution of the class, and that among the Endopterygota those orders in which the greatest difference exists between imago and larva - the Lepidoptera, Diptera and Hymenoptera - were the latest to take their rise.
Some of those zoologists who look to Peripatus, or a similar worm-like form, as representing the direct ancestors of the Hexapoda have laid stress on a larva like the caterpillar of a moth or saw-fly as representing a primitive stage.
The caterpillar, or the maggot, is a specialized larval form characteristic of the most highly developed orders, while the campodeiform larva is the starting-point for the more primitive insects.
Bionomically, metamorphosis may be defined as the sum of adaptations that have gradually fitted the larva (caterpillar or maggot) for one kind of life, the fly for another.
The oldest larva known, Mormolucoides articulatus, is from the New Red Sandstone of Connecticut; it belongs to the Sialidae, one of the lowest forms of Holometabola.
As the life-conditions and feedinghabits of the larva and imago become constantly more divergent, the appearance of the wing-rudiments would be postponed to the pre-imaginal instar, and that instar would become predominantly passive.
The Neuroptera, with their similar foreand hind-wings and their campodeiform larvae, seem to stand nearest to the presumed isopteroid ancestry, but the imago and larva are often specialized.
The antiquity of the Coleoptera is further shown by the great diversity of larval form and habit that has arisen in the order, and the proof afforded by the hypermetamorphic beetles that the campodeiform preceded the eruciform larva has already been emphasized.
In all the remaining orders of the Endopterygota the larva is eruciform or vermiform.
The eruciform larva of the Orthorrhapha leads on to the headless vermiform maggot of the Cyclorrhapha, and in the latter sub-order we find metamorphosis carried to its extreme point, the muscid flies being the most highly specialized of all the Hexapoda as regards structure, while their maggots are the most degraded of all insect larvae.
The Siphonaptera appear by the form of the larva and the nature of the metamorphosis to be akin to the Orthorrhapha - in which division they have indeed been included by many students.
In some way it is assured among the highest of the Hexapoda - the Lepidoptera, Diptera and Hymenoptera - that the larva finds itself amid a rich food-supply.
And thus perfection of structure and instinct in the imago has been accompanied by degradation in the larva, and by an increase in the extent of transformation and in the degree of reconstruction before and during the pupal stage.
Aristotle and Harvey (De generatione animalium, 1651) had considered the insect larva as a prematurely hatched embryo and the pupa as a second egg.
- Tarsal joint of an Ephemerid larva into which two Gordius larvae, (a,a) have penetrated.
In origin the vascular system is due to a fusion of spaces which arise in the mesoblast of the larva.
The larva of Cerebratulus is called the pilidium.
In accordance with these more sedentary habits during the first phases of life, the characteristic pilidium larva, which is so eminently adapted for a pelagic existence, appears to have been reduced to a close-fitting exterior layer of cells, which is stripped off after the definite body-wall of the Nemertine has similarly originated out of four ingrowths from the primary epiblast.
To this reduced and sedentary pilidium the name of " larva of Desor " has been given.
A curious feature shared by both larva and adult is the large size of many of the cells, e.g.
This is by far the largest family and contains the commonest species; the larva of Echinorhynchus proteus lives in Gammarus pulex and in small fish, the adult is common in many fresh-water fish: E.
angustatus occurs as a larva in Asellus aquaticus, as an adult in the perch, pike and barbel: E.
A, The larva of Echinorhynchus proteus from the body cavity of Phoxinus laevis, with the proboscis retracted and the whole still enclosed in a capsule.
Neorhynchus clavaeceps in Cyprinus carpio has its larval form in the larva of Sialis lutaria and in the leech Nephelis octocula: N.
The Tornaria larva offers a certain similarity to larvae of Echinoderms (sea-urchins, star-fishes, and sea-cucumbers), and when first discovered was so described.
As in the case of the Lamellibranchiata, the shell of the adult is not a direct derivative of the youngest shell of the larva.
By the aid of these cilia the larva swims actively, but owing to its minute size it covers very little distance, and this probably accounts for the fact that where brachiopods occur there are, as a rule, a good many in one spot.
After a certain time the larva fixes itself by its stalk to some stone or rock, and the skirt-like second segment turns forward over the head and forms the mantle.
The cirri or tentacles, of which three or four pairs are present, are capable of being protruded, and the minute larva swims by means of the ciliary action they produce.
Either before or just after turning, the mantle develops a larval shell termed the protegulum, and when this is completed the larva is termed the Phylembryo.
The larva now assumes specific characters and is practically adult.
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.
(From Morse.) A, Larva (neo-embryo) just come to rest.
I t may, however, be pointed out that Brachiopods seem to belong to that class of animal which commences life as a larva with three segments, and that tri-segmented larvae have been found now in several of the larger groups.
The egg gives rise to an oval larva, one half of which is ciliated and bears gland-cells, the opposite end carrying ten hooks.
The fate of the larva is unknown.
The transition of the larva from the intermediate to the final host is accomplished by the habits of carnivorous animals.
In most other cases the tail is not distinguishable, and the body of the larva is separable only into a scolex invaginated with a bladder (= hind-body and tail).
This form of larva is known as a cysticercus.
Of all parasites the one which by its mere presence is the most dangerous is the larva of Taenia echinococcus.
Cystotaenia coenurus, intestine of dog and wolf, larva (a coenurus, fig.
I A, Larva of Anopheles.
If in the course of the first twenty-four hours this larva meet with a tadpole it attaches itself at once and undergoes further development.
In the former case the larva creeps along the tadpole until it reaches the branchial opening into which it darts, fixes its sucker, and then throws off its cilia.
If successful, the larva throws off its cilia and develops a dorsal papilla, a median ventral sucker and an additional pair of lateral suckers.
From the egg a larva arises.
with the faeces of the host the larva hatches out and swims freely for a time.
In dry localities or in the absence of the intermediate host (usually a mollusc) this larva soon dies.
If, however, it encounters the host the larva bores its way in, and attacks the liver, mouth or gonad in which it comes to rest.
The cilia are lost, the eye-spots disappear, the digestive sac vanishes and the larva becomes a sac or "sporocyst" full of germ-cells.
According to some writers (Leuckart) they are derived from undifferentiated blastomeres, other authorities (Thomas, Biehringer, Heckert) trace them to the parietal cells of the larva.
By a series of changes similar to those by which the primary larva arose from a segmented egg, so do these secondary larvae or "rediae" arise from the germ-cells or germ-balls within the sporocyst.
The ciliated larva escapes from the egg into the water and enters an intermediate host (leech, mollusc, arthropod, batrachian or fish) where it undergoes a metamorphosis into a second stage in which most of the adult organs are present.
The Polyzoa are colonial animals, the colony (zoarium) originating in most cases from a free-swimming larva, which attaches itself to some solid object and becomes metamorphosed into the primary individual, or "ancestrula."
In the Phylactolaemata, however, a new colony may originate not only from a larva, but also from a peculiar form of bud known as a statoblast, or by the fission of a fully-developed colony.
This appears to indicate B that the Polyzoa are remotely allied to other phyla in which this type of larva prevails, and in particular to the Mollusca and Chaetopoda, as well as to the Rotifera, which are regarded as persistent Trochospheres.
II) constitutes the greater part of the larva and contains most of the viscera.
The larva swims by a ri ig of cilia, which corresponds with the praeoral circlet of a Trochosphere.
Kupelwieser, 18); but, like the alimentary canal and most of the other larval organs, it undergoes a process of histolysis, and the larva becomes the ancestrula, containing the primary brown body derived from the purely larval organs.
The alimentary canal, which may be represented by a vestigial structure, is accordingly not functional, and the larva does not become pelagic. A pyriform organ is present in most Gymnolaemata as well as the sucker by which fixation is effected.
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.
Finally, in the Phylactolaemata, the larva becomes an ancestrula before it is hatched, and one or several polypides may be present when fixation is effected.
The reproduction of tsetse-flies is highly remarkable; instead of laying eggs or being ovovivi parous the females deposit at intervals of about a fortnight or three weeks a single full-grown larva, which forthwith buries itself in the ground to a depth of several centi metres, and assumes the pupal state.
In the latter case the larva crawls about the bottom of the water or up the stems of plants, with its thickly-chitinized head and legs protruding from the larger orifice, while it maintains a secure hold of the silk lining of the tube by means of a pair of strong hooks at the posterior end of its soft defenceless abdomen.
Before passing into the pupal stage, the larva partially closes the orifice of the tube with silk or pieces of stone loosely spun together and pervious to water.
It is only necessary here to mention one anomalous form, Enoicyla pusilla, in which the mature female is wingless and the larva is terrestrial, living in moss or decayed leaves.
The feeding habits of the adult may agree with that of the larva, or differ, as in the case of wasps which feed their grubs on flies, but eat principally vegetable food themselves.
Not a few cases are known in which a parasitic larva is itself pierced by the ovipositor of a " hyperparasite," and even the offspring of the latter may itself fall a victim to the attack of a " tertiary parasite."
But the most natural division is obtained by the separation of the saw-flies as a primitive sub-order, characterized by the imperfect union of the first abdominal segment with the thorax, and by the broad base of the abdomen, so that there is no median constriction or " waist," and by the presence of thoracic legs - usually also of abdominal pro-legs - in the larva.
This sub-order includes the vast majority of the Hymenoptera, characterized by the narrowly constricted waist in the adult and by the legless condition of the larva.
- a, Pear Saw-fly (Eriocampoides limacina); b, larva without, and c, with its slimy protective coat; e, cocoon; f, larva before pupation; g, pupa, magnified 4 times; d, leaves with larvae, natural size.
The first larva is broad in front and tapers behind to a " tail " provided with two divergent processes, so that it resembles a small crustacean.
The eggs are laid in the nests of various bees and wasps, the chrysid larva living as a " cuckoo " parasite.
The prey is sometimes stung in the neighbourhood of the nerve ganglia, so that it is paralysed but not killed, the grub of the fossorial wasp devouring its victim alive; but this instinct varies in perfection, and in many cases the larva flourishes equally whether its prey be killed or not.
The female, instead of provisioning her burrow with a supply of food that will suffice the larva for its whole life, brings fresh flies with which she regularly feeds her young.
10) is a larva differing markedly in form from its parent, and adapted for a different mode of life, while the nymph before the final moult is sluggish and inactive.
a, Male; e, female; c, larva, magnified 20 times; b, foot of male; d, feeler of larva, more highly magnified.
Some are monothalamous, and contain but one larva of the gallmaker, whilst others are many-celled and numerously inhabited.
The larva of a New Zealand moth, Morova subfasciata, Walk.
Callimome regius, the larva of which preys on the larvae of both Cynips glutinosa and its lodger Synergus facialis.
In the development of the Hydrozoa, and indeed of the Cnidaria generally, the egg usually gives rise to an oval larva which swims about by means of a coating of cilia on the surface of the body.
Thus a planula larva may be a blastula, or but slightly advanced beyond this stage, or it may be (and most usually is) a parenchymula; or in some cases (Scyphomedusae) it may be a gastrula.
The gastrula has now become an actinula, which may be termed the distinctive larva of the Cnidaria, and doubtless represents in a transitory manner the common ancestor of the group. In no case known, however, does the actinula become the adult, sexually mature individual, but always undergoes further modifications, whereby it develops into either a polyp or a medusa.
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 Tubularia, on the other hand, the parenchymula develops into an actinula within the maternal tissues, and is then set free, creeps about for a time, and after fixing itself, changes into a polyp; hence in this case the planula-stage, as a free larva, is entirely suppressed.
The larva for a time swims freely in the sea-water, having a circlet of cilia round the body in front of the mouth, forming the velum.
He has observed that in young specimens of Siren lacertina (the larva is still unknown) the gills are rudimentary and functionless, and that it is only in large adult specimens that they are fully developed in structure and function; he therefore concludes that the sirens are the descendants of a terrestrial type of batrachians, which passed through a metamorphosis like the other members of their class, but that more recently they have adopted a permanently aquatic life, and have resumed their branchiae by reversion.
ment and of the struc ture of the disk to their identification of "trochus" and "cingulum" with the preoral and postoral wreaths of the trochophore larva.
8, D) (which has a male of the same type as Melicerta, &c.) is an extremely modified type, and its resemblance to the trochophore larva of Lepadorhynchus or Polygordius is only superficial.
The palps are really derived from part of the velar area of the larva.
The early larva of Anodonta is not unlike the trochosphere of other Lamellibranchs, but the mouth is wanting.
Other Lamellibranchs exhibit either a trochosphere larva which becomes a veliger differing only from the Gastropod's and Pteropod's veliger in having bilateral shell-calcifications instead of a single central one; or, like Anodonta, they may develop within the gill-plates of the mother, though without presenting such a specialized 210 1P -' 1 °* larva as the glochidium.
After the formation of the gastrula by epibole the larva becomes enclosed by an ectodermic test covering the whole of the original surface of the body, including the shell-gland, and leaving only a small opening at the posterior end in which the stomodaeum and proctodaeum are formed.
pallial suture and no siphons; freshwater; larva a glochidium.
They may be distinguished from the Neuroptera by the elongation of the head into a beak, the small prothorax, the narrow, elongate wings with predominantly longitudinal neuration, the presence of abdominal cerci and the cruciform larva.
Such organs are absent in Mollusca in the adult state, but a pair of nephridia usually occurs in the larva.
As in the Rotifera, it serves the veliger larva as an organ of locomotion.
They invariably disappear before the adult stage is reached, but their presence in the larva is evidence that the ancestral mollusc possessed a pair of true nephridia quite distinct from the coelomic excretory organs, which are so characteristic of existing forms in the adult condition.
The larva (fig.
The silk glands or vessels consist of two long thick-walled sacs running along the sides of the body, which open by a common orifice - the spinneret or seripositor - on the under lip of the larva.
As the larva approaches maturity these vessels become gorged with a clear viscous fluid, which, upon being exposed to the air immediately hardens to a solid mass.
When the larva is fully mature, and ready to change into the pupa condition, it proceeds to spin its cocoon, in which operation it ejects from both glands simultaneously a continuous and reelable thread of 800 FIG.
- Larva of Bombyx mori.
The mezankoorie moth of the Assamese, Antheraea mezankooria, yields a valuable cocoon, as does also the Atlas moth, Attacus atlas, which has an omnivorous larva found throughout India, Ceylon, Burmah, China and Java.
- Free-swimming Larva (Mailer's Larva) of a Polyclad Planarian to illustrate the trochosphere-hypothesis of the origin of Platyelmia.
The larva is seen in optical section, and its distinguishing feature is the ciliated lobed band (vl, sl, dl), which corresponds to the pre-oral ciliated band of a trochosphere-larva..
The Trochosphere-hypothesis (2), (3) is based chiefly on the occurrence in certain Polyclad Turbellaria, of a larval form (Miiller's larva) which is comparable to a certain stage (pro-trochula) in the development of the Trochosphere-larva.
This Trochosphere is the characteristic larva of Mollusca, Annelida T OT (After Abbott, T5ky5 Zool.
The importance of this resemblance between the Polyclad larva and the Trochosphere-larva of higher invertebrates is increased if the widely adopted V Ep (After F.
Antmimicry has also been recorded in the case of the larva of one of the Indian species of Mantidae.
Finally the larva of one of the Bornean Mantidae, which is a floral simulator in its pupal and adult stages, closely resembles in its black and red coloration the larva of the stinking and warningly coloured bug Eulyes amoena.
In the Hemipterous group of the Rhynchota ant-mimicry is illustrated by the larva of a British species of Reduviidae (Nabis lativentris) in which the forepart of the abdomen is furnished on each side with a patch of white hairs leaving a central narrow dark portion in imitation of the waist of the ant; and also by an East African species (Myrmoplasta mira) which in its general form exhibits a close resemblance to an ant (Polyrrhacis gagates) which occurs in the same neighbourhood.
Weismann, Lady Verney) have shown by experimenting upon birds that this suggestion is correct; and Guy Marshall found that baboons which are afraid of snakes are also afraid of the snake-like larva of the South African Chaerocampa osiris.
A parallel case of mimicry exists at Singapore between the larva of a Noctuid moth and the common red tree-ant (Oecophylla smaragdina).
In this case also the posterior end of the larva represents the anterior end of the ant.
An example of the latter occurs in Singapore where the vicious red spinning-ant (Oecophylla smaragdina) is mimicked by the larva of a Noctuid moth and by spiders belonging to two distinct families, namely, Saltiicus plataleoides (Salticidae) and Amyciaea forticeps (Thomisidae), there being no reason to suppose that either the moth larva or the spiders are protected forms. Mimetic aggregations of species similar to those mentioned above have been found in other countries; but the instances cited are sufficient to show how widespread are the influences of mimicry and how profoundly it has modified the insect fauna of various parts of the world.
- Fully formed larva of Echinorhynchus proteus from the body cavity of Phoxinus laevis (from Hamann).
The ectoderm behind the ciliated ring develops spicules, and the post-oral region of the larva elongates.
The trunk develops on the lower surface of the disk-like larva, which undergoes a more or less sudden metamorphosis into the young worm (fig.
The eggs are laid in the spring as a rule, and after about a week they give rise to a minute, ringed larva with a protrusible boring apparatus consisting of three chitinous rods.
By the aid of this the larva makes its way into the soft body of some insect larva, Ephemerids, Chironomids, or even of Molluscs, and encysts in the muscles or fat body.
The atrium or atrial chamber is a peripharyngeal cavity of secondary origin effecting the enclosure of the gill-clefts, which in the larva opened directly to the exterior.
The four principal phases in the development are: (I) Blastula, (2) Gastrula, (3) Flagellate Embryo, (4) Larva.
This becomes divided into two, the right half forming the cavity of the rostrum, while the left acquires an opening to the exterior, and forms the praeoral pit of the larva, which subsequently gives rise to special ciliated tracts in the vestibule of the mouth mentioned above.
Alcock (1901) describes from his own observation the newly hatched Phyllosoma larva of Thenus orientalis, Fabricius.
P. sylvestris in Britain is liable to many insect depredations: the pine-chafer, Hylurgus piniperda, is destructive in some places, the larva of this beetle feeding on the young succulent shoots, especially in young plantations; Hylobius abietis, the fir-weevil, eats away the bark, and numerous lepidopterous larvae devour the leaves; the pine-sawfly is also injurious in some seasons; the removal of all dead branches from the trees and from the ground beneath them is recommended, as most of these insects lay their eggs among the decaying bark and dead leaves.
C, Fixed larva.
The three pairs of appendages present in the " nauplius " larva show certain peculiarities of structure and development which seem to place them in a different category from the other limbs, and there is some ground for regarding the three corresponding somites as constituting a " primary cephalon."
4, larva of Apus cancriformis.
It is also found in the earliest and most primitive form of larva, known as the Nauplius.
The antennules (or first antennae) are almost universally regarded as true appendages, though they differ from all the other appendages in the fact that they are always innervated from the " brain " (or preoral ganglia), and that they are uniramous in the nauplius larva and in all the Entomostracan orders.
In the nauplius larva they lie rather at the sides than in front of the mouth, and their basal portion carries a hook-like masticatory process which assists the similar processes of the mandibles in seizing food.
In the Decapoda, where the antennal gland alone is well-developed in the adult, the maxillary gland sometimes precedes it in the larva.
A nauplius larva differing only in details from the typical form just described is found in the majority of the Phyllopoda, Copepoda and Cirripedia, and in a more modified form, in some Ostracoda.
It seems certain, therefore, that the possession of a nauplius larva must be regarded as a very primitive character of the Crustacean stock.
within the egg (or within the maternal brood-chamber), so that the larva, on hatching, has reached a stage more advanced than the nauplius.
Perhaps the most striking example is the zoea-like larva of the Sergestidae, known as Elaphocaris, which has an extraordinary armature of ramified spines.
So far as the zoea was concerned, this assumption was soon shown to be erroneous, and the secondary nature of this type of larva is now generally admitted.
kester FI c. - Larva of The former occur in all seas from the shore 3.
The larva is very common in hazel nuts and filberts.
The larva is a thick white grub with a brownish head, bearing fleshy tubercles along its side.
The nuts which are infested by this insect are usually the first to fall to the ground; the larva then bores a round hole through the nut shell, by means of its jaws, and creeps out.
Bruchus pisi causes considerable damage to pease; during the spring the beetle lays its eggs in the young pea, which is devoured by the larva which hatches out in it.
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).
The larva is provided with postoral and perianal ciliated bands, and on either side with a bunch of long provisional setae.
D, Larva of Myzostoma glabrum.
The larva, magnified.
In this larva four pairs of mesenteries having the typical Edwardsian arrangement are developed, but the fifth and sixth pairs, instead of forming couples with the first and second, arise in the sulcar chamber, the fifth pair inside the fourth, and the sixth pair inside the fifth.
C, Oral aspect of Arachnactis brachiolata, the larva of Cerianthus, with seven tentacles.
D, Transverse section of an older larva.
- Tangential section of a larva of Astroides calicularis which has fixed itself on a piece of cork.
Such a form as this is roughly represented to-day by the Actinotrocha larva of Phoronis, the importance of which has been brought out by Masterman.
But only slight modifications are required to produce the Tornaria larva of the Enteropneusta and other larvae, including the special type that is inferred from the Dipleurula larval stages of recent forms to have characterized the ancestor of the Echinoderms. We cannot enter here into all the details of comparison between these larval forms; amid much that is hypothetical a few homologies are widely accepted, and the preceding account will show the kind of relation that the Echinoderms bear to other animals, including what are now usually regarded as the ancestors of the Chordata (to which back-boned animals belong), as well as the nature of the evidence that their study has been, or may be, made to yield.
Lankester (2) was the first to suggest that (as is actually the fact in the Nauplius larva of the Crustacea) the prae-oral somites or prosthomeres and their appendages were ancestrally postoral, but have become prae-oral " by adaptational shifting of the oral aperture."
PHORONIDEA, a zoological order, containing a single genus Phoronis, which is known to be of practically world-wide distribution, while there are many records of its larva, Actinotrocha, from localities, where the adult has not been found.
The praeseptal cavity is a vascular space, since it is in free communication with the dorsal vessel of the larva, and it persists in part as the two lophophoral vascular crescents of the adult.
The relations of the surfaces after the metamorphosis are clearly very different from those which obtained in the larva.
Most observers consider that Actinotrocha is a highly modified Trochosphere, and this would give it some claim to be regarded as distantly related to the Entoproct Polyzoa and to other groups which have a Trochosphere larva.
After many years the larva is transformed into the pupa or nymph, which is distinguishable principally by the shortness of its antennae and the presence of wing pads.
When attacked by the disease, the larva moves uneasily, stretches itself out lengthwise in the cell, and finally becomes loose and flabby, an appearance which plainly indicates death.
The large and peculiar Archizoea gigas of Dohrn must, he thinks, belong to the Lepadidae as a larva in the last stage, but not, as v.
The larva can be found on young birch in July.
Figure 2. Evolution of positive birefringence in the maturing Drosophila larva.
caddis case before an experiment began and the mass of the larva at the end.
During pupation the larva undergoes complete metamorphosis, in which all its organs dissolve, leaving the pupa filled with fluid.
diploid zygote can only infect a mosquito larva.
The head of the cat flea larva is shown on the left.
The larva spins a very fine silken girdle to attach itself to the chosen pupation site.
Once the parasitoid larva hatches from the egg it will kill and consume the larva of the gall wasp.
larva of the rare marsh fritillary butterfly.
However, with no planktonic larva the dispersal of the mutation will be slow.
larva migrans Ã¢ this form of the disease develops due to severe or repeated toxocariasis infection.
Coming direct from a cave he found no mosquito larva or sea monsters present.
mayfly larva are very interesting for a study of the insect respiratory system.
midge larva makes a tunnel in the mud by sticking grains of mud together.
mosquito larva or sea monsters present.
moult larva's final molt is into a pupa, from which an adult emerges within a week.
moultthe first molt, the six legged larva turns into an eight legged nymph.
parasitoid larva becomes full grown and breaks out of the host which then usually dies.
whitefly larva finally pupating within the empty host skin as a light yellow ' mommy ' .
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.
- The fertilized ovum gives rise to a parenchymula, with solid endoderm, which is set free as a free-swimming planula larva, in the manner already described (see Hydrozoa).
In certain species of Myrmeleonidae, such as Dendroleon pantheormis, the larva, although resembling that of Myrmeleon structurally, makes no pitfall, but seizes passing prey from any nook or crevice in which it shelters.
The larva of a ground-beetle or a carnivorous waterbeetle (fig.
The fifth abdominal segment has a pair of strong dorsal hook-like processes, by means of which the larva supports itself in the burrow which it excavates in the earth, the great head blocking the entrance with the mandibles ready to seize on any unwary insect that may venture within reach.
The larva of Gyrinus (fig.
- In this tribe may be included a number of families distinguished by the softness of the cuticle, the presence of seven or eight abdominal sterna and of four malpighian tubes, and the firm, well-arm oured larva (fig.
15, b), emitting the well-known light (see above), is wingless and like a larva; the luminosity seems to be an attraction to the male, whose eyes are often exceptionally well developed.
The tenebrionid larva is elongate, with well-chitinized cuticle, short legs and two stumpy tail processes, the common mealworm (fig.
The phytophagous species are attached to various parts of plants, dead or alive; and the carnivorous in like manner feed on dead or living flesh, or its products, many larvae being parasitic on living animals of various classes (in Australia the larva of a species of Muscidae is even a parasite of frogs), especially the caterpillars of Lepidoptera, which are destroyed in great numbers by Tachininae.
(After Robert.) A, Nearly symmetrical larva f, Foot.
In the larva a nautiloid shell is developed which is coiled exogastrically, that is, dorsally, and the pallial cavity is posterior or ventral (fig.
In the larva there is no projection at the time the torsion takes place.
The transition from the free-swimming veliger larva with its nautiloid shell (fig.
Metchnikoff observed (1866) in the development of the parthenogenetic eggs produced by the precocious larva of the gall-midge Cecidomyia that a large " polar-cell " appeared at one extremity during the primitive cellsegmentation.
21, e) or saw-fly, with its long cylindrical body, bearing the six shortened thoracic legs and a variable number of pairs of " pro-legs " on the abdomen (this being the eruciform type of larva); the soft, white, wood?
In many aquatic larvae we find that all the spiracles are closed up, or become functionless, except a pair at the hinder end which are associated with some arrangement - such as the valvular flaps of the gnat larva or the telescopic " tail " of the drone-fly larva - for piercing the surface film and drawing periodical supplies of atmospheric air.
P. Marchal has (1904) described this power in two small parasitic Hymenoptera - a Chalcid (Encyrtus) which lays eggs in the developing eggs of the small moth Hyponomeuta, and a Proctotrypid (Polygnotus) which infests a gall-midge (Cecidomyid) larva.
A natural system must take into account the nature of the larva and of the metamorphosis in conjunction with the general characters of the imago.
Comparison of the tracheated wings with the paired tracheated outgrowths on the abdominal segments of the aquatic campodeiform larva of may-flies (see fig.
Further, although the wing-rudiments appear externally in an early instar of an exopterygotous insect, the earliest instars are wingless and wing-rudiments have been previously developing beneath the cuticle, growing however outwards, not inwards as in the larva of an endopterygote.
The larva is also armed anteriorly with a median piercing probe and a pair of sharp hooks by means of which it perforates the walls of the alimentary tract and makes its way into the body cavity, lungs or liver.
The larva is elongate and campodeiform.
The plankton is divided into (a) the Zoo-plankton (such as the minute crustacea and the eggs and larva of fishes and many other marine animals); and (b) the Phyto-plankton, that is, the minute algae, diatoms, peridinians, some flagellate protozoa, spores of alga, etc. The investigation of the plankton from a new point of view, begun by Hansen in 1889, was continued by Lohmann at Kiel, by Cleve in Sweden, by Gran and Ostenfeldt in Norway and Denmark, and by Herdman, Allen and others in England.
In these cases the larva, called Tornaria, is pelagic and transparent, and possesses a complicated ciliated seam, the longitudinal ciliated band, often drawn out into convoluted bays and lappets.
Segmentation is complete, a gastrula is formed, the blastopore closes, the archenteron gives off two coelomic sacs which, as far as is known, are unaffected by the super ficial segmentation of the body that divides the larva into three segments.
The walls of these sacs give rise at an early stage to muscles which enable the parts of the larva to move actively on one another (fig.
No stalk .1 has been seen by Simroth or Fritz Muller, but in other respects the larva r 2 resembles the stages in the development of Megathyris p and Terebratulina which immediately precede fixation.
Development of larva and seed go on together, a few of the seeds serving as food for the insect, which when mature eats through the pericarp and drops to the ground, remaining dormant in its cocoon until the next season of flowering when it emerges as a moth.
When swallowed by the final host such a " cysticercoid" larva evaginates its scolex, throws off its hooked vesicular tail, and begins to bud off proglottides at its free end (fig.
It is generally admitted that the larva of the Entoprocta (fig.
The pyriform organ has probably assisted the larva to find an appropriate place for fixation (cf.
As in the case of Cyphonautes, the larval organs degenerate and the larva becomes the ancestrula from which a polypide is developed as a bud.
The larva is soft-skinned (cruciform), being either a caterpillar (fig.
6, b) with numerous abdominal pro-legs, but in most families of Hymenoptera the egg is laid in such a situation that an abundant food-supply is assured without exertion on the part of the larva, which is consequently a legless grub, usually white in colour, and with soft flexible cuticle (fig.
The inquiline habit (" cuckoo-parasitism "), when one species makes use of the labour of another by invading the nest and laying her eggs there, is of frequent occurrence among Hymenoptera; and in some cases the larva of the intruder is not content with taking the store of food provided, but attacks and devours the larva of the host.
They are the " gall-flies," many of the species laying eggs in various plant-tissues where the presence of the larva causes.
It lives in the grub of a gall-midge and it ultimately becomes changed into the usual white and fleshy hymenopterous larva.
Besides the larva of the gall-maker, or the householder, galls usually contain inquilines or lodgers, the larvae of what are termed guest-flies or cuckoo-flies.
We homologize the rotifer with the Turbellarian larva (fig.
Other Lamellibranchs exhibit either a trochosphere larva which becomes a veliger differing only from the Gastropod's and Pteropod's veliger in having bilateral shell-calcifications instead of a single central one; or, like Anodonta, they may develop within the gill-plates of the mother, though without presenting such a specialized 210 1P -' 1 Ã‚°* larva as the glochidium.
The Sialidae or alder-flies (q.v.) differ from other Neuroptera in the jaws of the larva - which is aquatic, breathing by paired, jointed abdominal gills - resembling those of the imago, and being adapted for the mastication of solid food.
The Mantispidae are remarkable among the Neuroptera for their elongate prothorax, raptorial fore-legs and hypermetamorphic life-history, the young campodeiform larva becoming transformed into a fat cruciform grub parasitic on young spiders or wasp-larvae (see Mantis-Fly).
B, a, larvae boring their way into a root; b, larva of the immobile kind surrounded by the old skin, living as an ectoparasite on the outside of the root.
The same process, carried further, leads to the very peculiar larva known as the Zoea, in the typical form of which, found in the Brachyura (fig.
Thus, about 1875, the distinction of Echinoderms from such radiate animals as jelly-fish and corals (see Coelentera), by their possession of a body-cavity ("coelom") distinct from the gut, was fully realized; while their severance from the worms (especially Gephyrea), with which some Echinoderms were long confused, had been necessitated by the recognition in all of a radial symmetry, impressed on the original bilateral symmetry of the larva through the growth of a special division of the coelom, known as the "hydrocoel," and giving rise to a set of water-bearing canals - the watervascular or ambulacral system.
Known Echinoderms show the following features, imagined to be due to an ancestral pelmatozoic stage :- Increase in the coelomic cavities of the left side, and atrophy of those on the right; the dextral coil of the gut, recognizable in all classes, though often obscured; an incomplete secondary bilateralism about the plane including the main axis and the water-pore or its successor, the madreporite, often obscured by one or other of various tertiary bilateralisms; the change of the hydrocoel into a circumoral, arcuate or ring canal; development through a freeswimming, bilaterally symmetrical, ciliated larva, of which in many cases only a portion is transformed into the adult Echinoderm (where care of the brood has secondarily arisen, this larva is not developed).
On quitting the shelter of the parent tentacles the embryo becomes a pelagic larva, known as Actinotrocha (fig.
The abdomen under the wings of the butterfly still represents the larva.
After selecting a suitable site and sewing the front of the case shut, the larva pupates in the case.
The larva always feeds singly on the pith in the cavity of a teasel seedhead.
This hatches and feeds on the whitefly larva finally pupating within the empty host skin as a light yellow ' mommy '.
On occasion, tobacco beetles and their larva can infest cigars.
A microwave oven will kill any larva and eggs that might be in the cigars.
The mosquito ingests the larva of the worms that cause heartworm, known as microfilariae, when it bites an infected animal.
These differences in larval form depend in part on the surroundings among which the larva finds itself after hatching; the active, armoured grub has to seek food for itself and to fight its own battles, while the soft, defenceless maggot is provided with abundant nourishment.
But in general we find that elaboration of imaginal structure is associated with degradation in the nature of the larva, cruciform and vermiform larvae being characteristic of the highest orders of the Hexapoda, so that unlikeness between parent and offspring has increased with the evolution of the class.
If we admit that the larva has, in the phylogeny of insects, gradually diverged from the imago, and if we recollect that in the ontogeny the larva has always to become the imago (and of course still does so) notwithstanding the increased difficulty of the transformation, we cannot but recognize that a period of helplessness in which the transformation may take place is to be expected.
Moreover, in many insects with imperfect metamorphosis the change from larva or (as the later stage of the larva is called in these cases) nymph to imago is about as great as the corresponding change in the Holometabola, as the student will recognize if he recalls the histories of Ephemeridae, Odonata and male Coccidae.
Only a brief reference can be made here to the fascinating subject of the life-relations of the larva, nymph and pupa, as compared with those of the imago.
A common result of metamorphosis is that the larva and imago differ markedly in their habitat and mode of feeding.
The larva may be aquatic, or subterranean, or a burrower in wood, while the imago is aerial.
An interesting feature is the difference often to be observed between an aquatic larva and pupa of the same insect in the matter of breathing.
The gnat larva, for example, breathes at the tail-end, hanging head-downwards from the surface-film.
A marked disproportion between the life-term of larva and imago is common; the former often lives for months or years, while the latter only survives for weeks or days or hours.
The larvae produced by this remarkable method (paedogenesis) of virgin-reproduction are hatched within the parent larva, and in some cases escape by the rupture of its body.
In Tibicen septemdecim the life of the larva extends over from thirteen to seventeen years.
Larva campodeiform, usually feeding by suction (exceptionally hypermetamorphic with subsequent eruciform instars).
The most aberrant type of larva is that of the genus Prosopistoma, which was originally described as an entomostracous crustacean on account of the presence of a large carapace overlapping the greater part of the body.
By the pulsation of the pericardial vesicle (best observed in the larva) the blood is driven into the glomerulus, from which it issues by efferent vessels which effect a junction with the ventral (sub-intestinal) vessel in the trunk.
C, Larva of Stegomyia.
In the case of the pearl oyster this parasite is a cestode larva, but in the less valuable but no less genuine pearl produced by Mytilus, &c., the nucleus is a Trematode-larva (Jameson).
long) larva capable of swimming freely for a short time by the aid of five girdles of ciliated cells.
This very characteristic larva is termed a planula, but though very uniform externally, the planulae of different species, or of the same species at different periods, do not always represent the same stage of embryonic development internally.
Fertilization is external; and in about three days a small ciliated larva, not unlike that of the Echiuroids, but with no trace of segmentation, emerges from the egg-shell.
This little creature, which has many of the features of a Trochosphere larva, swims about at the surface of the sea for about a month and grows rapidly.
The larva is, hatched two or FIG.
(From Strubell.) B, First motile larva.
C, Second immovable parasitic larva casting its skin.
terga removed to expose the Gordius larva within.
The insect, which may have become an imago with the Gordian larva still in it, is then eaten by a carnivorous insect or by a fish, and the contained Gordian larva becomes elongate and mature in its second host.
After a year or more this larva emerges into the water and commences to reproduce.
a few cases, the parasitic bee grub devours not only the food-supply, but also the larva of its host.
- Larva and Pupa of Apis (magnified four times).
SL, Spinning larva.
FL, Feeding larva.
The nests of Andrena, for example, are haunted by the black and yellow species of Nomada, whose females lay their eggs in the food provided for the larva of the Andrena.
More violent in its methods is the larva of a Stelis, whose operations in the nest of Osmia leucomelana have been studied by Verhoeff.
Finally the parasitic larva attacks the Osmia, and digging its mandibles into its victim's head kills and eats it, taking from one to two days for the completion of the repast.
The female lays an egg in the unripe nut, on the kernel of which the larva subsists till September, when it bores its way through the shell, and enters the earth, to undergo transformation into a chrysalis in the ensuing spring.
It was not till Vaughan Thompson demonstrated, in 1830, their development from a free-swimming and typically Crustacean larva that it came to be recognized that, in Huxley's graphic phrase, "a barnacle may be said to be a Crustacean fixed by its head and kicking the food into its mouth with its legs."
From the foregoing epitome which applies to many species, Rhipicephalus appendiculatus for example, it is evident that every individual tick has to find a host on three occasions, namely, as larva, nymph and adult.
transforms the larva into the nymph takes place on the host, and in Margaropus annulatus the transformation of larva into nymph and nymph into adult is effected without the temporary sojourn on the ground.
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