SEX INHERITANCE 95 



subsequently disappear. In the toad .there is a 

 special enlargement at the anterior end of the 

 testis, called Bidder's organ, that is composed 

 exclusively of large egg-hke cells. The cells of this 

 organ may be the same as the scattered cells in the 

 testes of the young frog, which also occur sometimes 

 in the young toad. On the other hand the same 

 organ is found also in the young female toad, lasting 

 throughout the first year of her hfe. If it is an ovary 

 in the male, then the female would be said to have 

 two kinds of ovaries, one rudimentary the other 

 functional. 



In the lamprey (Petromyzon) the young males 

 also frequently have cells in their testes that appear 

 to be immature ova. Schreiner has shown that in 

 the hagfish (^Nlyxine) immature males have ova in 

 their testes, while immature females have young 

 sperm-cells in their ovaries. In this case the sexes 

 cannot be distinguislied until maturity. 



Certain teleostian fish pass through similar con- 

 ditions, but one teleost, Serranus, is described by 

 Dufosse and others as a true hermaphrodite. 

 . Whether the two following cases belong under 

 this heading may seem questionable. According to 

 H. N. Gould, the mollusc Crepidula plana is male 

 in the juvenile stage and female in later stages. 

 He finds that unless a young specimen is placed in 

 the vicinity of a larger individual the testes and 

 male genitalia fail to develop, and when the animal 

 grows older it develops ovaries and oviduct. But 

 in the presence of a larger individual the young 



