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-like 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 life. 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 (Myxine) immature males have ova in 
their testes, while immature females have young 
sperm-cells in their ovaries. In this case the sexes 
cannot be distinguished until maturity. 
Certain teleostian fish pass through similar con- 
ditions, but one teleost, Serranus, is described by 
Dufossé 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 
