CONJUGATION IN THE CRAYFISH, CAMBARUS AFFINIS 249 
hooks do not yield and as the thorax and abdomen are held as one 
piece by the contraction of the powerful muscles that connect 
them, the result of the unbending of the chelate legs is to depress 
the base of the abdomen, to force it nearer to the female. This is 
resisted by the rigid stylets, but if their tips are at the mouth of 
the receptacle they must be driven into it. 
This see-saw action of the whole animal that brings all the 
muscles into play to force the stylet to enter the annulus will be 
considered again after describing the anatomy of the hooks. 
To bring the organs to the position in which the actual transfer 
of sperm can take place thus requires the exertion of much mus- 
cular force in carrying out the instincts of the male. 
As will appear in another paper the mechanism of sperm trans- 
fer along the stylets is not completely understood. Besides the 
contractions of the sperm duct there are movements of advance 
and recession of the second stylet upon the first that have some 
significance and there is still another action, the movements of 
the abdomen that cause several successive short thrusts, or tamp- 
ing movements of the stylets. 
The last four phases — discharge of sperm, formation of plug 
withdrawal, liberation of female — were but little studied. Many 
hours are consumed before the sperm receptacle is quite filled, 
and the acutal packing of it is removed from observation. It 
does not appear that the sperm leaves the male till the stylet 
has found entrance into the annulus, and it is rare that any of the 
sperm escapes into the water. 
Normally all that is discharged goes into the receptacle, where 
sections show it arranged as if it had flowed in as a liquid mass. 
However, only the innermost part of the receptacle contains pure 
sperm and the outer parts are full of a secretion that is finally 
added in excess so that it protrudes from the mouth of the recep- 
tacle, as a sperm plug, that is evidence of conjugation having 
taken place. 
After the receptacle is filled the male reverses some of the pre- 
liminary phases by first raising the bases of the legs so that the 
hooks are disengaged from the grooves of the female's legs, then 
rising up away from the female, then crossing the fifth leg back 
