5 



chian selectei, Vlustelus canis of DeKay, is one in /»hich are 

 combined a structure fairly repre.~3entative of the Selachii as 

 a whole, a size convenient for work, and availability in suffi- 

 cient numbers to meet the rigorous demands of certain methods 

 of investii|atioa. 



This research was begun at the Marine Biological Laboratory 

 of Woods HolL, where two seasons were spent in the use of an 

 abundance of living material. The principal study was contin- 

 ued at the University of Iowa as my regular duties permitted; 

 while certain collateral lines were followed in the neurological 

 laboratory of the University of Chicago. A short preliminary 

 notice of the most important results then in hand was published 

 in the Proceedings of the Iowa Academy of Sciences, Volume IV. 

 The research has finally been brought to completion in the 

 biological laboratory of the Johns Hopkins University. 



It is a real pleasure to acknowledge my indebtedness to 

 the officials of the Marine Biological Laboratory for courte- 

 sies extending over a period of several years; and to Professor 

 Brooks, I cannot io less than express my sincere appreciation 

 of the numerous helpful suggestions given me during the com- 

 pletion of my work. 



