The détermination of sex in animal develoi)meut 711 



In 1879 in his work^) on the Daphnidae Weismann wrote: "an 

 explanation in the sense of a proof of the causes by which one egg 

 develops into a male, another into a female, cannot be given ; but it 

 cannot at present be demanded. Only so much can be established, 

 that fertilisation here has absolutely no influence on 

 the determination of sex, etc." 



Eecently in dealing with a dilï'erent case, the parthenogenesis of 

 the bee, his conclusion is the very opposite, for he writes: "Therefore, 

 I do not see how one can avoid the conclusion from the non-fertili- 

 sation of the eggs laid in drone-cells, that it is just the omission of 

 fertilisation, which here conditions the development into the male sex, 

 and conversely, that fertilisation of the egg at the same time deter- 

 mines the female nature of the embryo ('zugleich den Embryo zur 

 Weiblichkeit bestimmt'). How this comes about we do not understand : 

 but that there is a connection can no longer be denied." (Op. cit. 

 p. 499.) 



This conclusion cannot, I venture to think, commend itself to the 

 embryologist. Weismann's standpoint of 1879 would seem to be more 

 in accord with the facts. Dzierzon's theory ''^) of the determination 

 of sex in the bee by the occurrence or not of fertilisation is a con- 

 clusion purely of the post hoc order. It is not a generalization 

 applicable to all cases — even in the bee ! — and it does not ex- 

 clude other, and possibly more potent, determining factors. It would, 

 however, carry me too far to discuss the matter at this juncture. 



For reasons, to be presently briefly mentioned, its validity must 

 be denied, and with this the correctness of the idea of there being 

 any connection whatsoever between fertilisation and the sex of the 

 resultant offspring, not only in this instance, but in any case. 



1) Weismann, August, Beiträge zur Naturgeschichte der Daplinoiden, 

 Leipzig 1876—1879, p. 457. Also in: Z. wiss. Zool., V. 27—33. The 

 last paragraph is spaced in the original. 



2) A sharp distinction must be drawn between two things ; of 

 these the one is, that the eggs of bees, which produce drones, are not 

 fertilised, the other, that the absence of fertilisation is the cause of 

 the development of a drone out of such an unfertilised egg. The latter is 

 Dzierzon's theory of the determination of sex. To speak of the former 

 as "Dziekzon's theory" is to lead to needless confusion, and, moreover, 

 it is or is not a fact — not a theory — that as a rule the drone- 

 eggs of the bee are not fertilised. From the supposed fact of the ab- 

 sence of fertilisation Dziekzox set up the theory, that omission of 

 fertilisation in the bee determined the development to the male sex. 



