94 SEX INHERITANCE 
tion of F and M may be in hermaphroditic types, it is 
less inconsistent to use the symbols for the sex chro- 
mosomes as the symbols for the sex factors also, if 
it is at the same time recognized that the whole 
chromosome is not involved in determining sex. 
HERMAPHRODITISM AND SEX 
Typical hermaphrodites are individuals that ripen 
both eggs and sperm. They are found widely repre- 
sented in the plant and animal kingdoms, whole 
orders and classes consisting almost entirely of such 
individuals. Self-fertilization may occur, as in 
many plants, but cross-fertilization between different 
individuals appears more often to take place. In 
addition to these typical cases, that call here for no 
further comment, there are cases in which the in- 
dividual may ripen first its sperm and later its eggs 
(protandric hermaphroditism), or vice versa. There 
are also several cases in which, in the young stages, 
eggs (or egg-like cells) appear in a gonad that is 
found subsequently to function as a testis. In the 
amphipod crustacean, Orchestia gammarillus, Bou- 
lenger found that 198 out of 217 young males con- 
tained ova, or egg-like cells, in the testes. In the 
adult males these cells had almost completely dis- 
appeared. In the male harvestman (Phalangium) 
large cells, said to be eggs, have been found in the 
testes. In the testes of the young male frog of some 
species there are large egg-like cells in the testes 
just prior to the time of metamorphosis. They 
