552 W. L. TOWER, 



the air and evaporation, cause all of the solid part of the exuvial 

 fluid to coagulate and cement the appendages of the pupa fast to the 

 body and thus efiectually prevent any malformation of the delicate 

 pupal organs. While this cementing material is being deposited there 

 is also a rapid deposition of chitin, so that at the end of pupation 

 the pupa possesses a firm covering. If the newly transformed pupa 

 is immersed in pure water for a few moments, this cementing 

 material and some of the primary cuticula are dissolved and the 

 appendages are left free to assume any position, and hence to undergo 

 any amount of malformation. At this time the appendages are full 

 of haemolymph under considerable pressure, and as soon as they are 

 freed from restraint the blood pressure causes them to become malformed, 

 usually bladder-like. After the exuvial fluid has once hardened it is 

 not soluble in water, weak acids or alkalis. 



In beetles there is much variation in the amount of exuvial fluid 

 and the cementing of the appendages to the body. In species like the 

 CoccinelUdae which pass the pupal stage in the open air the appen- 

 dages are very firmly glued to the surface of the body. In species 

 which pass the pupal stage in a large cell the wings and legs are 

 usually fastened to the body. Species which pass their pupal stage 

 in narrow burrows as do most Cerambycidae and Buprestidae develop 

 but little exuvial fluid and there is almost no cementing of the 

 appendages to the body. 



During these last changes the wings become further difl'erentiated. 

 The elytra are thickened and the hind wings have become much 

 expanded and folded, but both are so much alike that the two are 

 almost indistinguishable in section. The wings are now large thin- 

 walled fluid-filled sacs, extremely delicate and easily malformed, and 

 without trace of adult structures; in this condition they pass on into 

 the final or pupal stage of development. 



10. Development in the Pupa. 



In the pupal stage the most important structures developed are 

 the rods of chitin-like material which pass from lamella to lamella 

 and prevent the wing from becoming malformed at the final trans- 

 formation. Immediately after pupation the hypodermal cells are found 

 in a single layer with a thin deposit of chitin over the outer ends, and 

 with the proximal ends of these cells prolonged into a dehcate struc- 

 tureless, fibre which connects the cell body with the middle or fused 

 basement membranes. In this condition the wing is a weak structure. 



