OBSERVATIONS ON COLEOPTERA. iSl 



tion would not be one of direct selective value and be greatly 

 developed by selection, because those individuals with an abun- 

 dant supply of exuvial fluid would have a far better chance of 

 passing safely these critical periods than those with a lesser supply 

 of the exuvial fluid. 



Changes in tJie Integument. - -In the integument the preparatory 

 changes preceding ecdysis begin before the larvae cease feeding 

 and consist largely in the withdrawal of the protoplasmic processes 

 of the hypodermal cells from the pore canals in the secondary 

 cuticula (Fig. 2, Z>) and the gradual change in the shape of the 



FIG. 4. C. jetnorata. Section in latter end of period of differentiation of last 

 instar, from the raesothorax. 



hypodermal cells whereby they become greatly elongated and 

 their outer ends and the basement membrane separated by two, 

 three or four times the usual distance. A section (Fig. 4) shows 

 this condition in which the hypodermis is in the form of a flat- 

 tened epithelium. 



The changes from the condition shown in Fig. 4 go on slowly 

 until at the beginning of the first contractions all the proto- 

 plasmic processes have been withdrawn and the hypodermis is 

 much thickened, due to the drawing away of the basement mem- 

 brane. With the first contractions the old cuticula and hypo- 

 dermal cells separate over almost the entire body surface and 

 only the muscle attachments remain to hold the old cuticula to 

 the animal. 



At the time when the contractions begin or slightly before, a 



