External Factors of Sex Determination 383 
the metamorphosis, which took place, in fact, — owing probably 
to the temperature, — two and a half to three months later than 
the others. Sections of the gonads showed 30 females, 26 males, 
and 1 hermaphrodite. 
The fourth lot, fed for some days on the jelly of their own eggs, 
were separated into three groups. The results were as follows : — 
Mates FEMALES Not DIFFERENTIATED 
Group I (vegetable food) 57 51 8 
Group II (animal food) 22 14 ° 
Group III (mud and their own 12. 23 ) 
dead) 
Groups I and II developed at the same rate. They were small, 
owing to the size of the aquarium, and underwent their meta- 
morphosis at the beginning of June. Group III was retarded. 
The tadpoles were small and had begun to die at the beginning of 
June. They were then fed on an animal diet, when they began 
to grow rapidly, and metamorphosed at the end of July. The 
frogs were small, and yet as the table shows there were more 
females than males, while in the case of those of Group IT that 
had animal food there are more males than females. In the case 
of Group I the two sexes are nearly equal in number. 
Cuénot points out that his own results as well as those of 
others are open to the serious objection that the sex of those that 
died is unknown, nevertheless he thinks that his experiments show 
that food is not a factor in determining the sex of tadpoles. 
The best-authenticated cases that seem to show the influence 
of food on the determination of sex are those of Hydatina senta 
and the daphnid, Simocephalus. The experiments that seem 
to establish this relation have been given in previous chapters. 
According to Nussbaum, the amount of food taken by Hyda- 
tina during the first few hours after hatching determines whether 
the kind of eggs laid will give rise to males or to females. This 
may mean either that all the eggs have their sex determined at 
this time, one way or the other, or that the food determines 
