5. General Conclusions and Summaries. o^ 



differs characteristically in the male and female. The presence of the parasite by interfering 

 with the metabolism of the body prevents the normal production of the characteristic sexual 

 substance, with the result that this substance is changed, causing in the female the atrophy 

 of the gonad and the secondary sexual characters, in the male passing from the highly diffe- 

 rentiated male condition to the more generalized hermaphrodite state. 



The great experience of Prof. Giard in the facts of parasitic castration, of which he 

 was the original discoverer, gives a corresponding weight to the theoretical conclusions which 

 he draws; it was therefore with great interest that I read a paper (12) recently published by 

 him and courteously sent to me, in which he considers the general question, how does castra- 

 tion affect the secondary sexual characters of an animal. The conclusions which he draws 

 are certainly negative, but not of less value for that reason. With perfect justice he argues 

 against the view that the secondary sexual characters are entirely controlled in their development 

 by a liquid substance (humorale) of the nature of a ferment circulating in the general fluids of 

 the body. The most weighty objection which he urges against this theory is the fact that 

 often a remarkable geometrical correlation appears to exist between the gonad and the secon- 

 dary sexual characters, such that the secondary sexual characters, of one side appear to be 

 correlated with the gonad of that side alone (as for instance in many abnormally hermaphro- 

 dite Lepidoptera), or the correlation instead of being lateral may be transverse. 



Since the theory that I have adopted must be placed in the category which accepts 

 the action of a liquid substance circulating in the body, I believe that Giakd's objection must 

 apply to this theory equally. I, moreover, fully agree with Giard that the correlation between 

 the primary and secondary sexual characters is not due to a specific ferment produced in the 

 gonad: and I think that the serious objection which he urges against the general theory of 

 specific liquids can be overcome in our theory by a little reflexion. 



According to the theory which I have sketched in this section the differentiation and 

 growth of both the primary and secondary sexual characters are due to a third common 

 factor, namely the evolution in the body of a sexual formative substance which may- 

 be either male or female or hermaphrodite. This substance, whose presence I infer from 

 the observations detailed in this chapter, I must also infer to be a fluid of some kind which 

 can be distributed to all the parts of the body, including the gonad, which can be affected by 

 sexual differentiation. 



But I cannot claim that the evolution of this substance is the sole factor; the other 

 factor must be, I think, a determinate differentiation of a certain degree which concerns the 

 cellular elements of the body. Thus, in an hermaphrodite Ascidian for example, I regard 

 the process of sexual differentiation as being due to tyvo factors, firstly the evolution of the 

 hermaphrodite sexual substance which circulates in the body and is the product of its meta- 

 bolism, and which becomes divided and distributed at maturity to the male and female cells, 

 and secondly a perhaps structural differentiation of these sexual cells of such a kind 

 that only those in a particular position and of a particular internal structure are capable of 



