OBSERVATIONS ON COLEOPTERA. 19! 



the specialization of the integument consists essentially, as I have 

 shown, in the development of a mechanical strengthening of the 

 body wall during ecdysis by the rearrangement of the hypodermal 

 cells in a very precise bridge-like structure ; the arrangement for 

 softening and dissolving a part of the cast chitinous covering, thus 

 decreasing resistance ; and finally the provision of a sufficient fluid 

 lubricator to enable the animal to slip out of its old covering with 

 the least danger of rupturing the body wall, or distortion of the 

 appendages. In these three provisions are features of great utility 

 which present many striking adaptations to the habits and habi- 

 tats of individual species. 



That ecdysis is a crucial period in the life of insect larvae is the 

 generally accepted belief, but how crucial is quite an open ques- 

 tion. During several years in which I have reared larvae of 

 Leptinotarsa for the study of their evolution I have found that 

 ecdysis is one of the phases on insect breeding needing most care- 

 ful attention. This is especially true in experiments wherein there 

 are used greatly changed conditions of existence, and the failure 

 of many experiments can be attributed directly to improper care 

 and surroundings during ecdysis. Even under normal conditions 

 each recurring cycle acts to eliminate from one to eight per cent, 

 of the larvae and the average per cent, of individuals in my experi- 

 ments with L. decimlineata, which cover eleven years, that were 

 killed during ecdysis alone, is 13.69 per cent. Often the per- 

 centage runs far higher, frequently lower, but even 13 per cent, 

 of a population is a huge death rate to be directly due to one par- 

 ticular process. The mortality from ecdysis occurs largely as 

 the result of failure to rupture the integument, due primarily to 

 its not becoming softened owing to the failure of the cuticula 

 solvents to develop. The larvae dying from this cause in insect 

 breeding are often passed over as belonging to the death rate of 

 a certain stage, while in reality it is largely the elimination due 

 directly to ecdysis. Comparatively few larvae die during ecdysis, 

 but about from I to 1.5 per cent, become deformed and die in the 

 following stage. Apparently none are killed during the recon- 

 struction stage, excepting by their enemies. If we knew the 

 whole history of say L. decimlineata, I think we should be very 

 near to the truth if we hold that in any given population 15 per 



