No. 3-] PHENOMENA OF SEX-DIFFERENTIATION. 483 



a view in which the maleness and the femaleness of the orsfan- 

 ism may be described as due to the dijfereiice of state in which 

 essentially the same organized matter appears as two different 

 organisms according to the different conditions in which it may 

 happen to be placed. The sexes, according to the latter view, 

 may be considered as two different aspects of one and the same 

 thing. The male and the female offspring of a given organism 

 both inherit a similar share of materials from both parents, but 

 simply take different courses in the mode of their ontogenetic 

 development. 



It is interesting in this connection to recall the beautiful experi- 

 ment of Maupas^ on the artificial determination of sexes in a Roti- 

 fer, Hydatina senta. The Rotifer, as is known, produces three 

 kinds of eggs, viz. two kinds of " summer eggs " and one kind of 

 "winter ^%%y Of the two kinds of " summer eggs," it is known 

 that the smaller ^g'g always gives rise to the male, and the larger 

 to the female. Under the ordinary circumstance, a certain 

 female Hydatina produces exclusively the female eggs, while 

 another female individual produces exclusively the brood of male 

 offspring. Taking advantage of this fact, Maupas tried a series 

 of experiments to determine under what circumstances this 

 exclusive production of the male and the female offspring comes 

 into play. Maupas holds, and his view seems to be amply 

 justified by the results of his experiments, that the ova of the 

 Rotifer up to a certain stage of their ovarian existence are devoid 

 of sex or are neutral. Once this stage is passed, they are fated 

 to develop either into the male or the female organism, as the 

 case may be. Maupas considers that the determining influence 

 which deflects the type of development of the organism, either 

 to the male or to the female side, is due to temperature. If 

 the ovarian ova which maintain the neutral stage as regards 

 their sex are exposed to the influence of a higher temper- 

 ature, they give rise to a far greater proportion of male organ- 

 isms ; while, on the contrary, if they are exposed to a lower 

 temperature, a far greater proportion of the offspring are 

 females. 



In his first experiment, Maupas took five young females of 

 Hydatina, and kept them in his laboratory, where the tempera- 



'^ Maupas, Stir la dctenninisme de la sexualite chez V Hydatina soila, Compc. 

 Rend. Acad. Sci., Paris, T. cxiii, 1891, 



