Development and Metamorphosis 



45 



Fig. 76. — Larva, pupa, and adult of 

 the tlesh-fly, Colli phora erylhroce- 

 phala, with complete metamor- 

 phosis. (Two times natural size.) 



larva is like that of a worm, to accompli.sh wriggling, crawling, worm-like 

 locomotion; in the adult it is very different, particularly in head and thorax; 

 the alimentary canal is usually adapted in the larva for manipulating and 

 digesting solid foods; in the adult, usually (except with the beetles and 

 a few other groups), for liquid food; there may be large silk-glands in the 

 larva, which are rarely present in the 

 adult ; the respiratory system of the larva 

 of some flies and Neuroptera is adapted 

 for breathing under water; this is only 

 rarely true of the adults. The heart 

 and the nervous system show lesser dif- 

 ferences, but even here there is no iden- 

 tity : the ventral nerve chain of the larvae 

 may contain twice as many distinct gan- 

 glia as in the adult. 



The larva lives its particular kind of 

 life: it grows and moults several times; 

 but externally it shows at no time any 

 more likeness to the adult than it did at 

 hatching. But after its last moult it ap- 

 pears suddenly in the guise of a partially 

 formed adult in (usually) quiescent mummy-like form, with the antennas, 

 legs, and wings of the adult folded compactly on the under side of the 

 body, and the only sign of life a feeble bending of the hind-body in re- 

 sponse to the stimulus of a touch. This is the insect of complete meta- 

 morphosis in its characteristic second stage (or third if the egg stage 



is called first), the pupal stage. The 

 mummy is called pupa or chrysalid. As 

 the insect cannot, in this stage, fight or 

 run away from its enemies, its defence 

 lies in the instinctive care with which the 

 larva, just before pupation, has spun a 

 protecting silken cocoon about itself, or 

 has burrowed below the surface of the 

 ground, or has concealed itself in crack 

 or crevice. Or the defence may lie in the fine harmonizing of the color and 

 pattern of the naked exposed chrysalid with the bark or twig on which it 

 rests; it may be visible but indistinguishable. The insect as pupa takes 

 no food; but the insect as larva has provided for this. By its greed and 

 overeating it has laid up a reserve or food-store in the body which is drawn 

 on during the pupal stage and carries the insect through these days or weeks 

 or months of waiting for the final change, the transformation to the renewed 



Fig. 77. — .\dult worker {a) and larva 

 (6) of honey-bee. (.\dult natural 

 size; larva twice natural size.) 



