150 Transactions of the Society. 



as are known to be effective in the case of fern prothallia, failed to 

 produce the least effect." 



19. The view that there are two kinds of ova, determined 

 ab initio as male-producers and female-producers, has found a 

 vigorous supporter in Beard, who finds visible evidence of this in 

 the skate. He maintains that the sex is determined when the 

 primitive germ-cells divide into oocytes. In liis 1902 paper on 

 " The Determination of Sex in Animal Development," Beard 

 scouted the idea of environmental interference with the deter- 

 mination of sex. " Any interference with, or alteration of, the 

 determination of sex is absolutely beyond human power. To hope 

 ever to influence or modify its manifestations would be not less 

 futile and vain than to imagine it possible for man to breathe the 

 breath of life into inanimate matter." To this, an experimenter 

 like Russo would answer that he has succeeded in effectively 

 interfering with the determination of sex. Although it may not 

 be possible to alter the bias of an egg which has become fixed as a 

 male-producer or a female-producer, it may be possible by altered 

 nutrition to change the proportions of these two kinds of eggs in 

 the maternal ovary, and it may be possible in other ways to change 

 the normal proportions of survival. 



20. We give one instance of the numerous facts that might be 

 cited as suggestive in connexion with the theory of two kinds of 

 ova determined in the ovary as male-producers and female-producers. 

 In the case of five eggs laid by a sparrow-hawk (according to 

 Shufeldtj, the first became a male, the second a female, the third a 

 male, the fourth a female, and the fifth a male — in regular alter- 

 nation. Yet these were produced in a short time from one ovary, 

 and probably fertilized by the same set of spermatozoa. 



21. Of much interest are the facts of Poly-embryony — the pro- 

 duction of multiple embryos from one ovum. In the armadillo 

 Praopus (Tatnsia) hybrida von Jhering found on two occasions 

 eight embryos within one chorion — presumably, therefore, from 

 one ovum — and all were males. In some parasitic Hymenopterous 

 insects, e.g. Encyrtus, investigated by Marchal and Bugnion, Lito- 

 mastix and Ayeniaspis, investigated by Silvestri, one segmented 

 ovum forms a group of embryo, all of the same sex — female if the 

 egg be fertilized, male if it be not fertilized. These facts suggest 

 that the sex of the offspring is quite determined in the egg. 



(b) Two kinds of Spermatozoa. 



22. In about thirty different kinds of animals, such as the 

 freshwater snail Pahidina, and the freshwater beetle, there are 

 dimorphic spermatozoa, and it has been suggested that each kind 

 is predisposed towards the development of one sex. There is 

 however, no definite evidence of this. 



