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 



Fio. 4o3. Larval forms of three species of Platyyaiter (after Ganin). a, b, <, Cyclops-like 

 larval stages 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 

 cephalic region, but the following thoracic and abdominal segments 

 are entirely without appendages. The larvae of the Weuroptera, 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 larvae, 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 



