356 IXSECTA. 



The metamorphosis of the second group, to which the higher 

 orders of the Insecta belong, is more complicated. The larva here 

 leaves the egg in a condition which often differs considerably from 

 that of the imago, not only in form, but also in manner of life. 

 This larval stage, which is characterised by the large amount of 

 nutrition taken, and repeated moults, attains a considerable size, and 

 finally changes into a resting or pupal stage. The faculty of loco- 

 motion is now suppressed ; the pupa hardly moves and takes no 

 nourishment ; all the animal processes step into the background, 

 while the vegetative processes bring about the further (chiefly 

 internal) changes in the body. The larval stage is thus followed 

 by one which in many respects resembles the embryonic stages ; 

 the pupal stage might be defined as a recurrence of embryonic 

 development. A certain distinction between the two is, however, 

 evident to the careful observer. In the embryonic stages, the organs 

 develop chiefly from uniform rudiments, whereas they are here often 

 built up by the concrescence of a number of disconnected formative 

 centres, the so-called imagined discs. These imaginal discs must 

 be regarded as persistent embryonic structures which have lasted 

 throughout larval life in a latent condition, and in which the 

 regenerative capacity of the embryonic rudiment has been retained. 

 Those organs, on the contrary, which functioned in the larva undergo 

 disintegration (p. 368). 



The pupal stage gives place, after another moult, to the stage of 

 sexual maturity, the winged imago-stage, during which there is no 

 further growth of the body. 



The Insects that develop according to this type are known as the 

 Heteromorpha, and their metamorphosis is a complete metamorphosis* 

 i.e., they belong to the Metabola or Holo-metaboJa. 



A. Homomorpha. 



The post-embryonic development of the Insects belonging to this 

 type is in most cases a true metamorphosis, in so far as the young 

 animal that emerges from the egg, although similar in other respects, 

 is distinguished from the adult by the absence of wings (and of 

 those abdominal appendages which are transformed into the external 

 genital organs). In some cases also, alteration in the manner of 

 life may be accompanied by changes in the form of the extremities 

 (Cicada). The transformation into the perfect Insect is gradual. 

 The last larval stage, with the rudiments of the wings already 

 developed, is known as the nymph or pupa. In the Pediculina 



