. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. LARVAL DEVELOPMENT. 549 common the uniform segmentation of the ganglionic chain. Never- theless, it is probable that only a proportionately few of the larval forms have preserved the primitive form, and have a phylo- genetic significance (Orthoptera). In most cases the insect larvae owe their special peculiarities to secondary adaptations. In exceptional cases, the metamorphosis may be distinguished by quite special larval forms, as for instance in the Pteromalina (Platygaster, Teleas), the
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. LARVAL DEVELOPMENT. 549 common the uniform segmentation of the ganglionic chain. Never- theless, it is probable that only a proportionately few of the larval forms have preserved the primitive form, and have a phylo- genetic significance (Orthoptera). In most cases the insect larvae owe their special peculiarities to secondary adaptations. In exceptional cases, the metamorphosis may be distinguished by quite special larval forms, as for instance in the Pteromalina (Platygaster, Teleas), the eggs of which are laid in other insect larvae (fig. 458). The lowest, usually parasitic larvae are quite vermiform, and are without limbs or a separate head, the latter being represented by the anterior rings of the body (maggots of Diptera and of numerous. FIG. 433.—Larval forms of three species of Platyjatter (after Ganin). a, b, r, Cyclops-like larval stage* with claw-like jaws, cephalothoracic shield and abdomen, d, second larval stage, e, Third larval stage. Hymenoptera, fig. 66, a). In other cases there is indeed a separate cephalic region, but the following thoracic and abdominal segments are entirely without appendages. The larvae of the Neuroptera, of many beetles, of the Tenthredinidce and butterflies (caterpillars), have, on the contrary, jointed appendages on their three free thoracic seg- ments, and frequently also a greater or less number of rudimentary appendages, the so-called prolegs, on their abdomen. There are two rudimentary antennae on the heads of these larvje, and a varying number of simple eyes. The mouth parts are, as a rule, adapted for biting, even when the adult animal has a suctorial tube, but, with the exception of the mandibles, they are usually rudimentary. The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not pe
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