262 
E. A. ANDREWS 
They arise in the first year and become more developed after 
their first use. 
The female has no special organ to receive the hooks, but the 
joint mechanism common to both sexes is used as a socket, which 
is efficient as long as the males and females keep their special 
postures in conjugation. 
The fifth leg of the male is also used as an auxiliary organ as 
it furnished mechanical support for the stylets. Its use on the 
right and the left is guided by remarkable actions of the male. 
The length of the claws of old males seems advantageous for 
carrying on conjugation. 
In conjugation there is a series of events advancing in orderly 
sequence to the transfer of sperm and then, in part, reversing. 
In this series there may be considerable trial of various organs at 
various stages and this varies with individuals and cases. 
The early stages of conjugation are carried out after the removal 
of the stylets has made the completion of the series impossible. 
Later stages are performed after removal of antecedent middle 
stages. After very imperfect expression of the first stages, later 
stages may follow as far as is mechanically possible. 
The male acts as if receiving accurate local stimuli. In autumn 
and winter and early spring the males respond eagerly to other 
crayfish and conjugation is accomplished wherever possible. 
The entire series of conjugative actions seems preexistent in the 
male to be awakened, at times, with explosive violence, on very 
slight stimulation. It is then carried out in its entirety whenever 
there is no mechanical obstacle. 
Sex ''recognition" exists, apparently, only in the sense that 
the male may carry out all the stages of conjugation if a female 
happens to be seized, but not if a male is seized. There is no 
sufficient evidence that the male recognizes the female as such, or 
as a whole. But the passive response of the female when seized 
makes the completion of the conjugation possible while the more 
effective resistance of the male when seized sooner breaks the 
series of conjugation acts. 
The receptors of the male affected by male and female as 
objects seized appear to be only those that are stimulated by 
