178 VERTEBRATE REPRODUCTIVE CYCLES 



ovulatory mechanism of the rabbit was first being studied 

 Villemin is reported^i to have expressed his complete 

 disbelief that a female v^^ould ovulate on being merely 

 ogled by a male in a nearby cage, but apart from the 

 fioweriness of the language this may indeed happen! 



These examples of nervous stimuli to the secretory 

 activity of the anterior pituitary are all taken from the 

 birds and mammals. As Burrows^^ says it is probable 

 that such stimuli play a greater role in the higher 

 vertebrates, although there is plenty of evidence that 

 they are important in the lower forms as well. In man 

 himself the balance between nervous state and reproduc- 

 tive capacity is also well known to medical men, and one 

 of the commonest causes of the stoppage of the menstrual 

 cycle is said to be nervous shock. 



12. CONCLUSIONS 



To draw together the evidence recorded in this 

 chapter is a particularly difficult task, but by omitting 

 details and ignoring controversy it may be attempted as 

 follows. 



The most fundamental point which has been estab- 

 lished is that the anterior pituitary is a control centre of 

 the reproductive processes, although it is perhaps itself 

 under the control of the hypothalamus (see p. 102). The 

 pituitary is undoubtedly the intermediary between the 

 external environment and the nervous system on the one 

 hand and the maturation and proper functioning of the 

 gonads on the other. In all cases which have been studied 

 the influence of the external environment reaches the an- 

 terior pituitary through the eyes, the optic nerves, and 

 the brain, but as other species with other habits come 

 to be studied other sense organs will undoubtedly be 

 found to be involved. 



The pituitary hormones stimulate the gonads in two 

 ways. First they cause them to secrete their own hor- 

 mones (androgens in the testis and oestrogens in the 



