364 



INSECTA. 



second stage (Fig. ISO D), and then the actual pupa (Fig. 180 E), which changes 

 into the imago. The freely moving as well as the resting stages are thus here 

 multiplied. 



Hymenoptera. The larvae of the Hymenoptera belong to various types. 

 The larvae of the Tcnthredinidae, which feed upon leaves, in appearance and 

 colouring resemble the Lepidopteran larvae, and are therefore called false 

 caterpillars (Fig. 181). They are distinguished from true caterpillars by the 

 possession of a single ocellus on each side of the head, and by the unusually 

 large number of abdominal limbs, the anterior pair belonging to the second, 

 and not, as in the true caterpillars, to the third abdominal segment. There 

 are generally six to eight pairs of abdominal appendages. An exception is 

 afforded by the genus Lyda, in which, besides the thoracic limbs, there is only 

 a pair of jointed appendages (cerci) at the posterior end of the body. These 

 false caterpillars resemble the larvae of the Uroccridae, which bore into wood, 

 but the latter are distinguished by the absence of eyes and of abdominal limbs. 

 Most of the other Hymenoptera have degenerate larval forms in consequence 

 of their peculiar and often parasitic or semi-parasitic manner of life. Whether 

 the larva develops in vegetable outgrowths (galls), like many Cynipidae, or 

 parasitically in other Insect larvae, like some Cynipidae, the Pieromalidae, 

 Ichitcumonidae, etc., or whether it finds nutritive material in the cells con- 

 structed and stored with food by the parent, or is fed during growth (Fossoria. 



Vespidae, Apidae, Formicidae) the 

 passivity connected with its manner 

 of life always brings about a reduc- 

 tion of the limbs and of the mouth - 

 parts, and an approximation to tin- 

 general appearance of the maggot. 

 In the larvae of Bees and AVasps, the 

 enteron remains closed posteriorly, 

 and does not communicate with the 

 proctodaeum which receives the Malpighian vessels. The pupal stage is 

 generally passed through within a spun cocoon. The pupa is free-limbed, and 

 resembles the imago in structure, since, when the larva passes into the pupa, 

 the limb-rudiments are only gradual!}' protruded from the imaginal disc 

 (pp. 371-374), the pupal stage is preceded by a form showing the limbs only 

 half protruded (Dewitz, No. 102), and it is this form that is known as the 

 semi-pupa, sub-nymph, or pro-nymph. 



The eggs of the Ichncumonidac, Braconidae, and Ttcromalidac develop in the 

 eggs or larvae of other Insects. The larvae of the Ichneumonidac are, as a rule, 

 maggot-like. They may, however, possess at the posterior end of the body 

 caudal appendages (Anomalon) or caudal vesicles (Microgastcr), which are lost 

 on entering the pupal stage. The Pteromalidae, on the contrary, undergo a 

 very remarkable metamorphosis. The ontogeny of these forms which has been 

 described by Filippi, Metschnikoff, Ganix, Ayehs, and Lemoine, is char- 

 acterised by the absence of nutritive yolk from the egg, by the absence or 

 imperfect development of the embryonic envelopes, by the early hatching 

 of the larva, and by the strange shapes of the larval forms. "We are still very 

 much in the dark as to the first stages of development. In Plaiygastcr, a 

 continuous process of division gives rise to numerous cells, some of which soon 

 become arranged to form a superficial layer which surrounds the embryo in the 

 form of an envelope (corresponding to the serosa). The other cells form the 



Fio. 181, — Eruciform larva of a Tenthridinid 

 (Trichiosoma Iticorum, after Westwood). 



