PEOGEESS OF INTEENAL CHANGES. 359 



(925.) After having attained the pupa state, the last steps of the 

 process are completed, and the dermic system becomes fully developed 

 in all its parts. The oral apparatus attains its perfect condition ; the 

 wonderfully-elaborate structure of the eyes is completed ; the antennae 

 assume their full development ; the legs, enclosed in those of the pupa, 

 attain their mature form ; and the wings, which have been continually 

 growing, although concealed in the wing-cases of the pupa, acquire their 

 ultimate size : the perfect insect is ready for liberation, and, enclosed in 

 its last covering, creeps out of the water in which it has so long resided, 

 to enter upon a new state of existence. Fixing itself upon some plant 

 in the neighbourhood of its birthplace, the imprisoned Dragon-fly splits 

 its pupa-case along the back (fig. 181, A), and slowly extricates its head 

 and body ; it then draws its wings from their coverings, and its legs from 

 those of the pupa as from cast-off boots ; and at length (fig. 181, B), get- 

 ting its body from its now useless covering, it becomes entirely free. 

 The wings, before soft and crumpled, slowly expand (fig. 181, c) ; the 

 nervures harden ; the extended membranes dry ; and in a short time the 

 winged tyrant of the insect world (fig. 146) commences his aerial career. 



(926.) A strong argument in favour of the above views concerning 

 the production of successive skins from the dermis is derived from the 

 phenomena attending the cure of wounds in insects. If a perfect insect 

 be wounded, the wound is never healed at all ; and if a larva or pupa 

 is similarly injured, the wound remains uncicatrized until the next 

 moult, when the newly-formed integument is found to exhibit no traces 

 of the injury. The secreted and extra- vascular cuticle cannot cicatrize ; 

 but the living and vascular dermis is not only able to repair injuries in- 

 flicted upon itself, but, in secreting the next investment, to obliterate all 

 indications of their occurrence. 



(927.) The changes above described are produced by the progressive 

 development of the dermic or tegumentary system, the parts of which, 

 as we have already seen, becoming strengthened and consolidated by 

 degrees, ultimately acquire that density of structure which the external 

 skeleton of the insect exhibits in its perfect or imago state. But while 

 this extraordinary metamorphosis is going on externally, other changes 

 not less important are in progress in the interior of the body. The size 

 of the alimentary canal, and the shape, proportionate dimensions, and 

 general arrangement of the different parts composing it are secretly 

 and imperceptibly undergoing variations in accordance with the altered 

 necessities of the animal. We have already seen a conspicuous example 

 of this in Lepidopterous insects, 916 ; and in other orders equally 

 striking instances might easily be selected. One of the most remark- 

 able is met with in many Hymenoptera, as, for example, in Bees (Apis), 

 Wasps (Vespa), and Ant-lions (Formka leo), as well as in most of the 

 Ichneumonidce. In all these genera, the larva being concealed in a 

 close cell during its development, under circumstances which would 



