102 POPULAR SCIENCE MONTHLY. 



fed) there were 51 females and 57 males (and 8 not differentiated). 

 The i^roportionate number of females to males in all the tadpoles 

 reared in these experiments is not different from that which Cuenot 

 determined in nature. He concludes from his results that the sex of 

 the frog is not influenced by the external conditions (especially of 

 food) to which the tadpoles are subjected. 



Pigeons have also furnished some interesting facts in regard to 

 problem of sex. From the time of Aristotle it has been recognized 

 that of the two eggs laid in each batch one generally produces a male 

 and the other a female. Nevertheless numerous exceptions have been 

 recorded in which both individuals were of the same sex. Cuenot 

 himself found in eight sets that in two instances there were two 

 males; in two instances there were two females, and in five instances 

 there was a male and a female.* It has been claimed moreover, and 

 the tradition also goes back to the time of Aristotle, that the first egg 

 laid gives rise to a male and the second to the female. Flourens con- 

 firmed this fact for eleven sets, and Cuenot found the same result. 

 The meaning of this is obscure, for it may be that a male Qgg is first 

 set free, or that the conditions to which the first egg that is laid is 

 subjected are such that it becomes a male. The former interpreta- 

 tion may appear to be the more probable, but it is not conclusively 

 established by the facts. 



Although many statistics have been brought together in regard to 

 the determination of sex in man and in other mammals there is no con- 

 vincing evidence showing that external factors determine the sex of 

 the embryo; and, as has been pointed out, there is strong evidence 

 pointing in the opposite direction. 



If we turn now to some of the lower animals we shall find that 

 there are a few indisputable cases in which it has been shown that 

 the sex of the individual is predetermined in the Qgg. It was dis- 

 covered by Korschelt that two kinds of eggs are produced by a small 

 worm, Dinophilus apatris, and that the larger eggs develop, after 

 fertilization, into females and the smaller into males. The females 

 are about 1.2 mm. long, while the males are only 0.04 mm. long. The 

 males are degenerate in structure; they are less numerous than the 

 females, and live only ten days, whereas the females live a month or 

 more. 



A similar difference in the size of the eggs that produce males and 

 females is found in certain rotifers, in Hydatina senta for example. 

 In this species there are three kinds of females distinguished by the 

 different kinds of eggs that they lay. One lays large eggs which 

 without fertilization produce females. Another lays small eggs, less 

 rich in j^olk than the last, and these eggs, also without being fertilized, 



* Tliere is here probably a misprint since 2 + 2 + 5 equal nine. 



