i 3 6 INSECT TRANSFORMATION 



behind the brain and beneath the gullet is a large, elongate 

 nerve-centre, representing the whole chain of ventral ganglia 

 fused together, paired nerves radiating from it to the 

 various segments of the larva. This highly-specialized con- 

 centration of the nervous system shows a marked contrast to 

 the typical, segmental arrangement in the Bibio larva de- 

 scribed above (p. 128). 



The series of insect larvae mentioned in this chapter illustrate, 

 it will be seen, an increasing divergence between the form 

 of the creature in its final winged condition and in its prepara- 

 tory state. The grub of the ground-beetle (see p. 100) with its 

 large, firm head-capsule, well-armoured body, and long legs 

 with two-clawed feet, differs far less from its parent than the 

 soft, degenerately modified, headless and legless maggot, that 

 we have just been considering, differs from the fly. The import- 

 ance of this graded array of larvae with their varying characters 

 has been recognized by all students of insect transformations, 

 though greatly divergent views have been held as to the inter- 

 pretation of the fact. At this stage of our discussion of the 

 subject it may suffice to call attention to two points. The 

 greatest difference between imago and larva is shown among 

 those insects that are most highly specialized structurally. 

 And where as in the case of the oil beetles and Mantispa two 

 or more larval forms occur in the same life-history, the active 

 armoured larva precedes the soft, legless grub in order of 

 appearance. 



B. DIFFERENCES AMONG PUPAE 



Among those insects whose wing-growth is of the hidden or 

 inward type, the pupa is a most characteristic stage in the 

 life-history. Its usually quiescent habit gives opportunity for 

 the transition from larva to imago. While less absorbing as an 

 object of study than the larva that precedes or the imago that 

 follows it, the pupa has many features of interest worthy of 

 attention. 



We have seen that the wings of insects of the group under 

 consideration become apparent at the pupal stage. Among 

 beetles (Fig. 56, /), lace wing-flies (Fig. 68 e), caddis-flies, 

 wasps and bees (Fig, 7ic), the pupal wings, as well as the 



