70 THE CLASS OF INSECTS. 



minute flattened portion. Tlie process of degradation here 

 seems carried out to its farthest limit. 



Thus the degraded forms of the lower series of Hexapods 

 take on a Myriopod aspect. In the more highly cephalized 

 Diptera, Lepidoptera, and Il3'menoptera the degraded forms 

 are modelled on a higher articulate type. The idea of a divis- 

 ion into three regions is involved. Thus the wingless forms 

 of Flies, such as the Bird-louse, Nirvms; the Bat-tick, Nycte- 

 ribiu; the Bee-louse, Braula; and Cliionea resemble strikingly 

 the biregional Arachnids. 



In the wingless female of Orgyia and the Canker-worm moth, 

 the head is free, but the thorax is merged into the abdomen. 

 The resemblance to the lower insects is less striking. The 

 worker ants and wingless Ichneumons, Pezomachus, still more 

 strictly adhere to the type of their suborder, and in them the 

 triregional form^^ the body persists. Among the first of the 

 examples here cited we have seen the workings of a law, by 

 which most degraded forms of insects (and this law is exerted 

 with greater force in Crustacea) tend to revert to the worm-like, 

 or, as we may' call it, the archetypcd^ form of all Articulata. 



We have seen that many winged forms mimic the groups 

 above them, whereas the wingless degraded species revert to a 

 worm-like form. In either case, the progress is towards a 

 higher or a lower form. The latter is the more exceptional, as 

 the evolution and growth of all animals is upwards towards a 

 more si)ecialized, differentiated form. 



The Imago. After completing its transformations the adult 

 insect immediately seeks to i)rovide for the propagation and 

 continuance of the species. The sexes meet, and, soon after, 

 the male, now no longer of use in the insect economy, perishes. 

 The female hastens to lay her eggs either in, upon, or near 

 what is to be the food of the young, and then dies. This 

 l)eriod generally occurs in the summer and autumn, and during 

 the winter the species is mostly represented b}^ the egg alone. 

 Rarely does the adult insect hibernate, but in many species 

 the pupa hibernates to disclose the adult in early summer. 

 The larva seldom, as such, lives through the winter. 



Re'auraur kept a virgin butterfly for two years in his hot- 

 house. From this it would seem that the duration of the life 



