I 



REPRODUCTION AND SEX 493 



other internal secretions. But it is indisputable that they exert a 

 particularly strong and definite formative influence on certain parts 

 — and these are the sex-characters. The difficulty is to understand 

 the history of this correlation. 



STATEMENT OF KAMMERER^S CONCLUSIONS.— The first 

 important step in the evolution of sexual reproduction was the 

 specialising of germ-cells as distinguished from body-cells. The 

 second was the differentiation of dissimilar gametes — contrasted 

 in their assimilation capacities, amount of cytoplasm, size, and 

 activity — the microgametes and the macrogametes which unite in 

 fertilisation. The differentiation of sex doubtless occurred very early 

 in phylogeny, and the determination of sex often occurs, as we shall 

 notice later, very early in ontogeny. It is progamic or syngamic; 

 the future sex of the organism is usually quite settled at fertilisa- 

 tion. Before this, during the maturation period, the gametes are 

 probably in varying degrees susceptible to external influence, so that 

 their predisposition or bias to one sex or the other (eingeschlecht- 

 licher Entwicklungstendenz) may be changed (it is to be supposed 

 that they all have the primordia of both sexes), but the higher the 

 animal the less is this susceptibility. Only in plants and in the lower 

 animals can we succeed in experimentally changing the progamic 

 predisposition, activating the tendency which should otherwise be 

 latent. The factors that condition maleness ("Mikrogametismus") 

 or femaleness ("Makrogametismus") are ultimately assimilation- 

 differences. Here Kammerer agrees with the thesis of our Evolution 

 of Sex (1889). 



Removal of the essential gonads changes the metabolism, affects 

 the whole body, and is usually followed by degeneration of the sub- 

 sidiary and incidental sex-characters. But this cannot be used as a 

 criterion to distinguish sex-characters and body-characters. It seems, 

 in fact, as though the body was "sexed" through and through. 



But the castration, however early it may be, never prevents the 

 appearance of the embryonic primordium of any character. The 

 absence of the gonad has a purely quantitative effect on the degree 

 of development which a character may reach, or on the degree of 

 regeneration which may occur after loss. When the essential gona- 

 dial substances are introduced in any form (by transplantation, 

 injection, etc.) into a castrated animal, the effects of castration are 

 alleviated or reversed. 



Breeding experiments show that sex-characters behave in in- 

 heritance like all other specific or racial characters. They illustrate 

 either blended or alternative inheritance. Moreover, hybridising 

 experiments show that indifferent systematic characters may come 

 to be sex-linked, and conversely that the characters of one sex may 

 come to be the common property of both sexes, or may wholly 



