42 2 Expei'ifnental Zoology 



that the protoplasm has two possible ways of differentiating 

 which are determined by local conditions, internal or external. 

 The same ways of conceiving the problem may be appHed to the 

 case of sex determination. 



Which of these alternative interpretations we may think more 

 probable, or more profitable as a working hypothesis, is perhaps, 

 at present, a question of personal choice ; for we lack, as I have 

 said, the data to decide between them. For myself, the physio- 

 logical conception seems more in accordance with our general 

 ideas concerning development, and above all to be a conception 

 that is more stimulating and suggestive as a working hypothesis 

 than the morphological idea, which seems to be quite sterile as a 

 point of view leading to further investigation. 



Analysis oj the Results 



An analysis of the evidence that has been given in the preced- 

 ing pages concerning sex determination suggests the following 

 considerations. 



The average equahty of males and females indicates, I think, 

 that external conditions do not regulate the result, but that some 

 internal physiological mechanism exists that determines the sex.* 

 This physiological mechanism does not involve the separation 

 of male and female elements or units in the egg and sperm, but 

 only involves the production of those conditions that determine 

 whether one or the other sex will develop. In some cases the 

 initiatory processes may exist in the egg, in others in the sperm, 

 and in still others after the union of egg and sperm. In other 

 words, in all species with separate sexes the potentiaHties of pro- 

 ducing both sexes is present in all eggs and in all sperm ; but the 

 development of the one or the other sex is determined by some 

 unknown internal relation. From this point of view it is mis- 

 leading to speak of male and female eggs or sperm in the sense 

 that such eggs contain only male or female potentialities, for all 



^ Of course this statement does not exclude the possibility that external in- 

 fluences may not determine that the internal mechanism shall become active 

 in one way or another as seen in the cyclical modes of reproduction. 



