The determination of sex in animal development. 761 



that employed by Nature in both animals and plants it must be 

 obvious, that one simpler and better calculated to suit the end is 

 hardly conceivable. 



SuniDiary of Chief Conclusions. 



Reviewing briefly the ground covered in preceding pages, it is 

 seen, that sex in its origin from a primeval isogamy was bound up 

 with the constant differentiation of fourfold gametes. These were such, 

 that two of them, the female- and the male-eggs, were ultimately 

 formed within a sterilised Metazoan person, the female, while the 

 development of the remaining two, the two kinds of spermatozoa, was 

 alloted to a similar but not identical person, the male. The gametes 

 of the female, that is, the two forms of eggs, possessed functions 

 different from those of the two kinds of spermatozoa of the male, and 

 for this reason alone a sexual difference between the male and the 

 female, a dimorphism, was bound to follow. Of the twofold gametes 

 of the male it is to all appearance rare at the present time to find 

 the full and complete differentiation of both in any given case, but 

 this is known to happen in Paludina vivipara, Fygaera bucephala, 

 and a few other instances. In others one form of male gamete under- 

 gones more or less complete suppression in the course of the sper- 

 matogenesis, thus in Cicada, Bufo calamifa, Hyla, Bana esculenta etc., 

 the degree of degeneration varying in different cases. Though never 

 of functional value — unless it take the place of the ordinary form 

 of sperm — the second kind of spermatozoon is probably always 

 represented by something in every Metazoan spermatogenesis, its 

 development must at least be initiated, but it may be arrested anywhere 

 in the history of the spermatogonia, or in the spermatocytes. It is 

 the task of the functional spermatozoon to bring about the effects due 

 to amphimixis. 



Since it is the egg, which develops, and not the sperm, the burden 

 of providing for the continuance of the race falls upon the female Meta- 

 zoon, or rather upon the germ-cells, of which it is the host. To carry 

 out this duty the differentiation of twofold gametes, the male- and the 

 female-eggs, is needful. The germ-cells of the female thus make 



in later life a greater proportion of female-eggs than of male ones. If 

 female infanticide were very general in China, the race would infallibly 

 die out, for no females would be left; those murdered are such as, 

 owing to the prevailing social conditions, would produce no offspring. 

 Obviously, this example proves the truth of the thesis up to the hilt. 



