422 Experimental 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 applied 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 of 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 equality 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 potentialities 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 
1 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. 
