CHAPTER IV 



HORMONES AND REPRODUCTION 



I. INTRODUCTION 



DURING the last thirty years the increase in our 

 knowledge of the physiology of vertebrate repro- 

 duction has been overwhelming, and to-day it is almost 

 more than one person can do to continue to evaluate the 

 spate of new information that is constantly pouring out 

 in many languages from many countries. In these 

 circumstances the present chapter offers little more than 

 the merest introduction to the subject; it is a picture 

 painted in the broadest outlines. For those who would 

 go further there are many more detailed reviews, of 

 which the most generally useful are the two books of 

 Allen*, ^ and, more recently, those of Burrows,^^ and 

 Robson,^^^ and especially Parkes.^^^ 



In disentangling the physiological processes that 

 initiate and control reproduction, it is necessary first to 

 consider briefly the structures of certain organs, and 

 then, in more detail, the ways in which these organs 

 function and the influences which they exert on each 

 other and on the body in general. Such influences are 

 usually exerted by means of chemical substances known 

 as hormones, which are formed by internal secretory 

 glands, also called endocrine glands. These substances 

 have been classified by Huxley, ^^^ -^ho has defined a 

 hormone *as a chemical substance produced by one tissue 

 with the primary function of exerting a specific effect 

 of functional value on another tissue'. Some of these 

 substances may diffuse directly through the tissues, but 

 the commonly known hormones, including those men- 

 tioned below, are transported round the body in the 

 blood and lymph. 



