254 General Discussion 



Mullerian ducts. In mammals, the Mullerian system is derived from 

 both pronephric and mesonephric rudiments, whilst in elasmobranch 

 fishes it arises by longitudinal splitting of the Wolffian ducts. Con- 

 sequently, the part played by the ovary, in furthering Mullerian 

 differentiation whilst suppressing Wolffian development, might 

 repay further study. Furthermore, the employment of the methods 

 of tissue culture, using synthetic media, should as Dr. Price rightly 

 emphasizes, greatly advance the study of ageing and differentiation. 



Jost gave numerous data on the effects of decapitation on mam- 

 malian foetuses, especially rabbits and rats. In particular he called 

 attention to the importance of the pituitary for testicular develop- 

 ment and for controlling liver glycogen. The stepwise utilization of 

 hormones by the growing foetuses, as well as the limited period of 

 action of the foetal endocrines struck me as points of particular 

 interest. Perhaps the manner of utilization of hormones are neces- 

 sary evolutionary steps and their abolition would prevent evolution. 

 However, while it is impossible to deny the importance of the foetal 

 endocrines, I am convinced that their limited period of action and 

 the further fact that they act during periods of great sensitivity of 

 the target organs, are in some way implicated with the endocrine 

 functions of the placenta. 



There exists a widespread belief among laymen, as well as among 

 biologists, that single and multiple congenital malformations are 

 always the result of changes in the germ plasm, in other words, 

 they are genetically determined and hereditary. While we must not 

 for a moment minimize the importance of genetic factors in the 

 causation of congenital abnormalities, it must be realised that de- 

 velopmental processes can be altered by environmental disturbances 

 as well as by abnormal genes. Thus Jost demonstrated certain 

 teratological effects in rats which result from the administration 

 of pitressin and cortisone ; pitressin producing amputations if given 

 before the sixteenth day of pregnancy and cortisone producing cleft 

 palate. I do not believe that these are specific effects, nor should 

 they be regarded as senescent changes. 



Turning now to a consideration of glycogen metabolism, it may 

 be no coincidence that foetal rabbit liver begins to store glycogen on 

 the twenty-fifth day of pregnancy, for as Prof. Wislocki reminds us 

 Claude Bernard was the first to propose that the placenta was a 

 deputy for the foetal liver, until such time as the latter was physio- 

 logically capable of forming and storing glycogen. Consequently, 

 since glycogen storage in rabbit foetal liver may be postponed by 

 decapitation, it would be pertinent to know whether the placenta 

 still retained its glycogen storage functions when the foetal liver 

 was so influenced. 



