The determination of sex in animal development. 719 



Notwithstanding the expenditure of labour for an apparently 

 negative result, I am very glad to have carried out the count here. 

 At any rate it has prohibited any erroneous generalization, that the 

 number of primary germ-cells of the female is always double that of 

 the male. Moreover, the find has served to help to clear up certain 

 cases of twofold gametes, simulating hermaphroditism, in the males 

 of certain species. 



Of these there may be here mentioned 1) the presence of ap- 

 parently true eggs in the testis of the lamprey, P. planeri^ and of the 

 common toad, Bufo vulgaris, and 2) the two kinds of spermatozoa 

 — the wormlike and the hairlike or ordinary forms — in certain 

 snails, Paludina vivipara, AmpuUaria, Murex brandaris, and in 

 a moth, Pygaera bucephala, etc. These, and possibly very many 

 other cases, may be interpreted as eithisr abortive, or futile, attempts 

 on the part of the male to differentiate t/wo sorts of gametes. But 

 it must be insisted, that nothing goes to show both ever to be of 

 functional import. 



As to the "eggs" of the testis, of course, these are not "eggs". 

 Like the instances of apparent eggs in the testis of Bana esculenfa, 

 or in its fatty bodies, of both of which the writer has seen several 

 cases, they are merely spermatogonia, or spermatocytes of the first 

 generation. Being such, they are the true "homologues" ^) of ovarian 

 eggs. I regard these and other instances of the usual or the sporadic 

 production of "eggs" in the testis as abortive or useless gametes, or 

 the forerunners of such, of a second form ^). In the toad, and prob- 



1) The writer feels unable to maintain the existing embryological 

 opinion of the complete homology of the sexual products of the male 

 with those of the female. 



2) The reader may be reminded, that abortive and useless gametes 

 are not treated of here for the first time: embryologists have long re- 

 cognised their general occurrence in the conjugation of the Protozoa, 

 and in the formation of the "polar bodies", separated by every oocyte 

 in the Metazoa tefore it becomes an egg, capable of fertilisation. 



Apart from degeneration of germ-cells at various periods of the 

 cycle — of which, while it is by no means uncommon (e. g., Ascaris^ 

 Salamandra), no estimate has yet been made in any single instance — 

 it must now be recognised, that in all cases of spermatogenesis 'with 

 twofold spermatozoa, fully differentiated, there is always one abortive 

 gamete more than obtains in the formation of an egg from an oocyte, 

 i. e., in the shape of the three polar bodies. But while, for example, 

 in the "ripening" of a male- and of a female-egg in Paludina there 

 may be six abortive gametes, in the corresponding period in spermato- 



