IQ2 W. L. TOWER. 



cent, are on the average eliminated by the process of ecdysis and 

 the accidents which may occur along with it. 



Ecdysis is, in fact, extremely important in the physiological 

 activities of insects, each recurring period being accompanied by 

 great disturbances in all parts and functions of the body besides 

 those described in this paper. Muscles, digestive apparatus and 

 excretory system are deeply influenced by the process, and in 

 some forms at least are the seat of developmental dangers occur- 

 ring also in rhythmic cycles. 



As far as my experience and observations go ecdysis is a pecu- 

 liar process which periodically reduces various organs and parts 

 of organs to a condition strongly resembling an undifferentiated 

 embryonic condition from which are again built up old or new 

 characters by exceedingly rapid reconstructive processes, each 

 passing through in its development, stages seen in the develop- 

 ment of the same or similar earlier larval characters. This 

 repetition of stages in the development of colors or other char- 

 acters is solely due to the recurrent rhythmic processes necessary 

 to further growth and development. Ecdysis is a process of in- 

 tense importance in the life of the individual and generation and 

 one upon which natural selection can work most effectively. This 

 preliminary paper suffices to call attention to the importance and 

 deep-seated nature of ecdysis in insect economy, the general fea- 

 tures of the internal changes accompanying this process, some 

 of its most striking anatomical changes and its direct selective 

 value in the evolution of insects. 



HULL ZOOLOGICAL LABORATORY, 

 THE UNIVERSITY OF CHICAGO, 

 February 6, 1906. 



