certain that there is no int., pelagic larval form.
Some members of this order spend the winter in the adult state, others in the " larval " or " pupal " condition.
The parasitic and free-living Nematodes are connected by transitional forms which are free at one stage of their existence and parasitic at another; they may be divided into two classes those that are parasitic in the larval state but free when adult, and those that are free in the larval state but parasitic when adult.
Mermis (in the larval state) is confined to the Invertebrata and Sphaerularia to bees.
the ground and the young larvae make their way into grasshoppers, in whose bodies they pass most of their larval life.
Although several species belonging to the second class occasionally enter the bodies of water snails and other animals before reaching their definitive host, they undergo no alteration of form in this intermediate host; the case is different, however, in Filaria medinensis and other forms, in which a free larval is followed by a parasitic existence in two distinct hosts, all the changes being accompanied by a metamorphosis.
They, however, show no periodicity, and are found continuously both by day and by night; and their larval forms are termed Microfilaria perstans.
A third form, Microfilaria diurna, is found in the larval stage in blood, but only in the daytime.
After the second larval moult, he passes through a passive stage comparable to the pupa-stadium of an b insect, and during this stage, which occurs inside the root, the reproductive organs are perfected.
solid larval tentacles, re Radial nerve.
preceded by six per cartilaginous margin of the radial and six interradial disk centripetally in the solid larval tentacles).
The sensory cells are slender epithelial cells, often with a cilium or stiff protoplasmic process, and should perhaps be regarded as the only ectoderm-cells which retain the primitive ciliation of the larval ectoderm, otherwise lost in all Hydrozoa.
In Cunina parasitica, however, the ovum develops into an actinula, which buds actinulae as before, but only the daughter-actinulae develop into medusae, while the original, parent-actinula dies off; here, therefore, larval budding has led to a true alternation of generations.
This must not be taken to mean, however, that the medusa is derived from a sessile polyp; it must be regarded as a direct modification of the more ancient free actinula form, without primitively any intervening polyp-stage, such as has been introduced secondarily into the development of the Leptolinae and represents 'a revival, so to speak, of an ancestral form or larval stage, which has taken on a special role in the economy of the species.
The development of the Trachomedusae, so far as it is known, shows an actinula-stage which is either free (larval) or passed over in the egg (foetal) as in Geryonia; in no case does there appear to be a free planula-stage.
The actinula, when free, may multiply by larval budding, but in all cases both the original actinula and all its descendants become converted into medusae, so that there is no alter nation of generations.
Laennec to the hydatid, immature or larval tapeworm.
Strictly speaking, however, the term ant-lion applies to the larval form, which has been known scientifically for over two hundred years, on account of its peculiar and forbidding appearance and its skilful and unique manner of entrapping prey by means of a pitfall.
As regards growth after hatching, all beetles undergo a "complete" metamorphosis, the wing-rudiments developing beneath the cuticle throughout the larval stages, and a resting pupal stage intervening between the last larval instal1 and the imago.
Such a typically "campodeiform" grub, moving actively about in pursuit of prey, is the one extreme of larval structure to be noticed among the Coleoptera.
Whatever may be the true explanation of stridulating organs in adult beetles, sexual selection can have had nothing to do with the presence of these highly-developed larval structures.
Preferable to Lameere's system, because founded on a wider range of adult characters and taking the larval stages into account, is that of H.
The most interesting of the Heteromera, and perhaps of all the Coleoptera, are some beetles which pass through two or more larval forms in the course of the life-history (hypermetamorphosis).
The first larval stage is the "triungulin," a tiny, active, armoured larva with long legs (each foot with three claws) and cercopods.
After a resting (pseudo-pupal) stage and another larval stage, the pupa is developed.
This is followed by a resting (pseudo-pupal) stage, and thisby two successive larval stages like the grub of a chafer.
The wasps are said to leave the larval or pupal Metoecus unmolested, but they are hostile to the developed beetles, which hasten to leave the nest as soon as possible.
27), and allied genera - feed both in the adult and larval stages, on dung or decaying animal matter.
They are vegetable feeders, both in the perfect and larval stages, and are often highly injurious.
Any organism may pass through a series of free-living larval stages.
In the Cyclorrhapha on the other hand, in which the actual pupa is concealed within the hardened larval skin, the imago escapes through a circular orifice formed by pushing off or through the head end of the puparium.
To a geographical distribution of the widest extent, Diptera add a range of habits of the most diversified nature; they are both animal and vegetable feeders, an enormous number of species acting, especially in the larval state, as scavengers in consuming putrescent or decomposing matter of both kinds.
No specialized system of spermathecae, sperm reservoirs, and copulatory apparatus, as in Oligochaeta; development generally through a larval form; reproduction by budding also occurs.
larval form which is hatched at an early stage in development.
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.
The insects in the larval or wireworm stage attack the roots of plants, eating them away below the ground.
Larval " weevils " mostly feed on the roots of plants, but some, such as the nut weevil (Balaninus nucum), live as larvae inside fruit.
The most important Hymenopterous pests are the sawflies or Tenthredinidae, which in their larval stage attack almost all vegetation.
These two-winged insects attack all kinds of plants, and also animals in their larval stage.
Many of the adults are bloodsuckers (Tabanidae, Culicidae, &c.); others are parasitic in their larval stage (Oestridae, &c.).
Large pits are dug across the line of advance of these great insect armies to stop them when in the larval or wingless stage, and even huge bonfires are lighted to check their flight when adult.
This acts as a larval heart, but ceases to pulsate after a time.
Similar larval nephridia occur in other Gastropoda.
Enderlein and C. Bdrner (1904), and they are very evident in larval may-flies.
Sharp (1898), the marked divergence among the Hexapoda, as regards life-history, is between insects whose wings develop outside the cuticle (Exopterygota) and those whose wings develop inside the cuticle (Endopterygota), becoming visible only when the casting of the last larval cuticle reveals the pupa.
In other insects the imaginal disks are less completely disconnected from the superficies of the larval hypodermis, and may indeed be merely patches thereof.
The process of destruction of the larval tissues was first studied in the forms where metamorphosis is greatest and most abrupt, viz.
Many larval Hexapods might be defined in similar general terms, unlike as they are to their parents in most points of detail.
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.
Among a few of the beetles or Coleoptera, and also in the neuropterous genus Mantispa, are found life-histories in which the earliest instar is campodeiform and the succeeding larval stages eruciform.
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.
The presence of the two successive larval forms in the life-history constitutes what is called hypermetamorphosis.
In conjunction with the association mentioned above of the most highly developed imaginal with the most degraded larval structure, it indicates clearly that the active, armoured grub preceded the sluggish soft-skinned caterpillar or maggot in the evolution of the Hexapoda.
After a prolonged aquatic larval and nymphal life-history, the winged insect appears as a sub-imago, whence, after the casting of a delicate cuticle, the true imago emerges.
In the metabolic Hexapoda the resting pupal instar shows externally the wings and other characteristic imaginal organs which have been gradually elaborated beneath the larval cuticle.
Generally the larval is the feeding, the imaginal the breeding, stage of the life-cycle.
Thus a mass or chain of embryos is produced, lying in a common cyst, and developing as their larval host develops.
Young animals always unlike parents, the wing-rudiments developing beneath the larval cuticle and only appearing in a penultimate pupal instar, which takes no food and is usually passive.
Pupa incompletely obtect or free, and enclosed in the hardened cuticle of the last larval instar (puparium).
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.
The Odonata are in many imaginal and larval characters highly specialized; yet they probably arose with the Ephemeroptera as a divergent offshoot of the same primitive isopteroid stock which developed more directly into the living Isoptera, Plecoptera, Dermaptera and Orthoptera.
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.
Swammerdam, however, showed the presence under the larval cuticle of the pupal structures.
NEMERTINA, or Nemerteans (Nemertea), a subdivision of worms,' characterized by the ciliation of the skin, the presence of a retractile proboscis, the simple arrangement of the generative apparatus, and in certain cases by a peculiar pelagic larval stage to which the name " pilidium " has been given.
Both Hetero- and Metane- mertini have been more exhaustively studied than the other two groups, the first, as was noticed above, being characterized by peculiar larval forms, the second developing without metamorphosis.
- The same, in the first larval stage; under side.
After a series of moults it passes into the second larval stage, somewhat like the parent but differing in having each integumental ring armed with a fringe of backwardly directed short bristles.
The adult stage, for example, has been found in the nasal passages of sheep, goats, horses and even of man, and the larval stage in the pleural and peritoneal cavities of dogs and cats.
All the species are usually infested with Cercariae and Rediae, the larval forms of Trematode parasites of vertebrates.
polymorphus, larval host the crayfish, adult host the duck: E.
moniliformis has for its larval host the larvae of the beetle Blaps mucronata, for its final host certain mice, if introduced into man it lives well: E.
Gigantorhynchus gigas lives normally in the pig, but is not uncommon in man in South Russia, its larval host is the grub of Melolontha vulgaris, Cetonis auratus, and in America probably of Lachnosterna arcuata: G.
Sexually mature whilst still in the larval stage.
Neorhynchus clavaeceps in Cyprinus carpio has its larval form in the larva of Sialis lutaria and in the leech Nephelis octocula: N.
The larval forms are provided with eye-spots, but no very specialized sense organs are found in the adult.
Plankton Expedition, ii., 1897) has described, a few larval brachiopods of undetermined genera, two of which at least were pelagic, or at any rate taken far from the coast.
Naturg., 1861-1862), have their mantle turned over their head and the larval shell well developed.
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.
- Shell of larval Brachiopod.
A large number of specimens of a species are usually found together, since their only mode of spreading is during the ciliated larval stage, which although it swims vigorously can only cover a few millimetres an hour; still it may be carried some little distance by currents.
He discovered (1823) the Pentacrinus europaeus, and showed that it was the larval form of the Feather-Star Antedon (Comatula).
Mailer's studies on the larval forms of Echinoderms and the discoveries of Vaughan Thompson were appreciated.
But whilst in Trematoda a digestive sac is invariably present except in the sporocyst larval stage, the Cestodes possess no trace of this organ at any stage of their development.
The life-history of Cestodes consists of larval and adult stages, which are usually passed through in different hosts.
Here it develops into a larval, or rather an adolescent form.
The peculiar feature of the larval history of Cestodes is the development in most cases of a cyst or hydatid on the inner wall of which the scolex is formed by invagination.
We have, in fact, a form of larval multiplication that recalls the development of digenetic Trematodes.
both adult and larval, contain toxins of great virulence, though in.
I I) in the brain of sheep; allied forms occur mature in the dog and larval in the rabbit.
The Euculicidae are divided into the Asiphonatae (=Anophelinae), the larvae of which have no respiratory siphon, and the Siphonatae, or forms in which a respiratory siphon is present in the larval state.
In Europe and North America the continued existence of species is ensured by the hibernation of impregnated females, or else the winter is passed in the egg or occasionally in the larval state.
The rapid multiplication that takes place in the larval stage of nearly all endoparasitic forms affects the tissues of the "intermediate" host in which they live.
Von Linstow has indeed suggested that Gyrodactylus is a larval form capable of reproduction by an asexual method.
Here it gives rise by a peculiar process to numerous individuals of a second larval form, and these usually produce a third form from which the minute immature Trematode is developed.
The liver-fluke (Distomum hepaticum) passes through its larval stages in the water snail Limnaea truncatula in Europe; in L.
Others again consider that the whole cycle is a metamorphosis which, beginning in the Heterocotylea as a direct development, has become complicated in the Holostomidae by a larval history, and finally in the Malacocotylea has acquired additional complexity by the intercalation of two larval forms, and is thus spread over several generations.
This is followed by the atrophy of many of the larval organs, including the brain, the sense-organ and the ciliated ring.
The alimentary canal persists and revolves in the median plane through an angle of 180°, accompanied by part of the larval vestibule, the space formed by the retra^tion of the oral surface.
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.
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