TEE DETERMINATION OF SEX. loi 



proportion sometimes obtained when tadpoles are reared from egg& 

 artificially fertilized. 



Yung found that females of Eana esculenta are twice as numerous 

 as males, while Cuenot found, on the contrary, in a different locality 

 that there were more males than females.* It is not known whether 

 this disproportion in the sexes is due to the greater mortality of one 

 sex, or whether there are more eggs of one kind than of the other. 

 The results appear to indicate, however, that external conditions do not 

 have a determining influence on sex, and it seems not improbable, 

 although not completely established, that there may be greater mor- 

 tality among the male tadpoles than among the females in some species 

 and in certain localities. 



Cuenot made a few experiments with the eggs of Rana temporaria. 

 He points out that his results are open to the same grave criticism as 

 are those of his predecessors in that he did not determine the sex of 

 those that died. In one experiment in which the tadpoles were given 

 an abundant supply of vegetable food they suffered greatly from crowd- 

 ing and from insufficient aeration of the water. Their development 

 was retarded and they remained small. Of the 26 frogs that meta- 

 morphosed all were females. In another similar experiment there were 

 3 females and 4 males. In a third experiment the tadpoles were placed 

 in a large aquarium supplied with cold, running water. No food was 

 given, and the tails of the tadpoles were frequently amputated in order 

 to prolong the larval period. There emerged 57 young frogs, of which 

 33 were females, 29 males, and one hermaphrodite. 



In a fourth experiment the tadpoles were separated into three lots. 

 The first were given a vegetarian diet; the second were given only 

 animal food; and the third were put into a large aquarium whose 

 floor was covered with mud, but no food was present. The tadpoles 

 that died were no doubt eaten by their companions and thus a certain 

 amount of food was probably obtained. 



The first and the second lots developed at the same rate, but the 

 tadpoles did not reach a large size owing to the small dimensions of 

 the aquarium. They became frogs after two months. Those of the 

 third lot on the contrary were retarded in their development; they re- 

 mained small and began to die from hunger after the third month. 

 They were then given animal food; they grew rapidly and metamor- 

 phosed a month later, i. e., four months after hatching. The frogs were 

 of small size and showed signs of having been poorly nourished. Of the 

 35 survivors of this third lot 23 were females and 12 were males. Of 

 the 36 s^^rvivo^s of the second lot (with animal diet) there were 14 

 females and 22 males. Of the 108 survivors of the first lot (vegetarian 



* Boulenger also found in Pelodytes, Pelohates and Bufo an excess of adult 

 males. 



