INTRODUCTION 



Brown-Sequard, the first to prepare testis extracts, used 

 them on himself for the treatment of senility, and endocrino- 

 logy owes much of its rapid development to anthropocentric 

 interest. Most of the work, however, has been carried out on 

 the smaller mammals, which are so much more accessible than 

 man, and in more recent years endocrine processes in non- 

 mammalian vertebrates have also been increasingly studied. 

 This last branch of investigation is still in its initial stages. 



In 1935 the present authors began to investigate the sexual- 

 endocrine organization of non-mammalian vertebrates, and 

 this led to the establishment, in 1939, o^ ^^^ "Werkgemeen- 

 schap voor Endocrinologie" (Working Community for 

 Endocrinology) at Utrecht, under the auspices of the late 

 Professor H. J. JORDAN and Professor ChR. P. RAVEN. The 

 purpose of the present work is to summarize the material 

 dealt with and the work done during the war-years 1940 — 

 1945. Where necessary, reference is made to previous work. 



One difficulty met with when investigating the sexual- 

 endocrine organization of non-mammalian vertebrates is that 

 the phenomena to be studied are far less conspicuous than in 

 mammals. On the other hand, the smaller dimensions and 

 greater simplicity of structure of the organs are advantages. 



It would be unsafe, however, to draw conclusions, in 

 regard to possible analogies, from similar phenomena 

 observed in mammals and non-mammals. On closer examina- 

 tion it may appear that such phenomena show quite essential 

 differences. A typical example of this is given below. 



Fleischmann and Kahn (1932) must be given credit for 

 introducing the female bitterling (Rhodeus amarus, Bloch) 

 as a test animal for the study of sexual endocrinology. The 

 bitterling is a Cyprinid fish, found fairly generally all over 

 the Western part of continental Europe. In spawning time, 



