762 JOHN BEARD, 



provision not only for a new batch of female-eggs, but also for one 

 of male-eggs. The determination of sex for the next generation thus 

 lies with the germ-cells of the female Metazoan organism. 



In all dioecious Metazoa three kinds of functional gametes are 

 constantly needed and differentiated, of these two arise in the female, 

 one in the male. 



The actual determination of sex is initiated at the division of 

 the primary germ-cells into secondary ones: it is completed at the 

 formation of the oocytes and spermatocytes, and its manifestation is 

 accomplished by the numerical reduction of the chromosomes in these. 

 The determination does not come about in the primary germ-cells, 

 for if one of these undergo independent development alongside the 

 embryo, the result is the bringing forth of identical twins. All known 

 cases of like-twins are of the same sex, and from this it follows with 

 absolute certainty, that the primary germ-cells are alike in sexual 

 potentialities as in other respects. From a host of evidence it is 

 certain, that the determination of sex does not take place later than 

 the formation of the oocytes and spermatocytes. The history of the two 

 sorts of eggs of Raja hatis, Hydatina senta, Phylloxera, und DinopJiïlus 

 gyrociUatus, and that of the twofold spermatozoa of Paludina vivi- 

 para and Pygaera hucepliala, suffice to demonstrate the truth of this. 



Hermaphroditism is associated with the partial or complete 

 suppression of one form of gamete, the male-egg: parthenogenesis, on 

 the other hand, entails the occasional, or the cyclical, arrestment of 

 one or other of the two gametes of the female. If it ever become 

 acyclical with the consequent disappearance of the males, with these 

 there vanish the male-eggs, which produce them, and the spermatozoa. 

 That is, in such instances the only functional form of gamete left is 

 the female-egg, with which there remains no other form of gamete to 

 unite. (Actually, there is union with a polar body [Boveei] — a 

 form of isogamy.) 



Of very great importance for many questions is the recognition, 

 that any particular form of gamete may undergo suppression at any 

 period of the life-history; thus, in some instances of the rare production 

 of male persons their occasional appearance is undoubtedly due to the 

 omission to suppress one or more of the forerunners of male-eggs. 

 Similarly, the rarity or the apparent absence of a second form of 

 spermatozoon is readily explicable. 



Since there is no qualitative mitosis subsequently to the formation 

 of oocytes and spermatocytes, all four products of any one of these 



