20 
SIDNEY I. KORNHAUSER 
somes in hermaphroditism is scant, it is hardly worth while at 
present to speculate on the mechanism which produces such 
individuals. 
That the sexual tendencies of hermaphroditic forms is often 
in a sensitive balance, influenced by external conditions, is shown 
by the experiments of Baltzer on Bonellia and Gould on Crepi- 
dula. In Bonellia there are produced minute motile larvae 
with hermaphroditic potentialities. If the free swimming larvae 
find the proboscis of a female Bonellia, they attach themselves 
and develop into minute males after a parasitic existence of 
about four days. If, however, no proboscis is found, the motile 
larva sinks to the bottom and develops into a female. In this 
case we may say that probably some secretion from the pro- 
boscis of the female stimulates the development of the male 
anlage and that this is accompanied by the suppression of the 
female fundaments. Likewise the absence of the proboscis 
secretion allows the female fundaments to develop while those 
of the male are suppressed. Intermediates were produced by 
Baltzer by allowing larvae to attach to a proboscis and then re- 
moving them at intervals of less than four days. In Crepidula 
plana, a hermaphroditic gasteropod which is normally a pro- 
tandric hermaphrodite, Gould has shown that the presence of 
older individuals in the female state of development causes the 
production of sperm in small individuals nearby. Isolated small 
individuals, however, omit sperm production and form ova. 
Here is an animal in sensitive balance influenced by a secretion 
which probably comes to it through the sea water. The prob- 
lem of hermaphroditism, its mechanism and relationship to 
bisexual reproduction, is well worthy of intensive study. From 
such exceptions to the general rule we may hope to learn much 
about the normal mechanism of sex-determination. 
9 . CONCLUSION 
Finally, one may ask can sex ever be controlled? There seem 
to be two avenues of approach. In forms in which the female 
is heterogametic, external conditions may control maturation 
