246 
E. A. ANDREWS 
abdomen. Crayfishes have the habit of swinging back and forth 
the small appendages found under the abdomen; in the female 
this serves to aerate and clean the eggs and embryos when they 
are attached to these appendages, but at other times, and in the 
male at all times, it is not obvious what use the swinging motions 
of the ^^swimmerets" may be. However, when the peculiar male 
appendages are to be used the entire series is set swinging and the 
first and second partake of this motion enough to be raised from 
their usual position to the one of use in sperm transfer. These 
two appendages at rest are carried by the male forward, hori- 
zontally, in the deep groove under the thorax where they are con- 
cealed and protected. However, at this stage of conjugation they 
are lifted up by their muscles, or really swung downward and back- 
wards as far as their stiff basal joints will allow, only about 45 
degrees from the horizontal. A slight muscular movement serves 
to place the second appendage against the first so that it locks 
into it. The normal position of these organs is horizontal and 
they tend to return to it, but during the following hours of con- 
jugation they are held up by a remarkable device that relieves 
the weak muscle that elevates the stylet from the task of holding 
the stylet erect. The male with difficulty and care crosses either 
the left or the right, or sometimes first one and then the other 
of the last or fifth legs, under his thorax, in spite of the near 
presence of the body of the female that makes it awkward to 
swing the limb across; and thrusts it over between himself and 
the female till it lies as flat as possible under his thorax with the 
terminal joints protruding beyond the opposite side of the body. 
Henceforth in conjugation the male seems, at first sight, to lack 
the fifth leg on one side (fig. 1), while careful observation shows 
its tip on the other side. Either first or later trial has placed this 
leg across anterior to the erected stylets, and in this position this 
leg holds the stylets mechanically firm and erected at 45 degrees 
till the end of conjugation, when the leg is moved back and the 
stylets allowed to fall into their usual horizontal position of rest. 
Often, however, during the early stages of conjugation the male 
will try first one and then the other of the fifth legs in the attempt 
to carry on the chain of reflexes to the consummation of the fit- 
ting of the stylet into the receptacle. 
