1895.] Embryology. 869 
This unusual position of the leg secures the proper position and di- 
rection of the intromittent organs. These are the first and second pairs 
of pleopodes, or abdominal appendages. They normally lie forward in 
a horizontal groove beneath the thorax, but now they are depressed at 
an angle of about 45°, and are held so by the transversely placed leg, 
as may be seen from Fig. 1, which shows the white tips of the intro- 
E. 2. 
mittent organs of the left side. When the organs are thus held they 
may accomplish their purpose, which is to transfer the sperm to the an- 
nulus of the female. 
As seen in Fig. 2 the abdomen of the female is bent up, and that of 
the male partly surrounds it. At times the male relaxes the abdomen 
and moves forward upon the female. Ultimately the two are so accu- 
rately adjusted—and this is a difficult problem in two such irregular, 
rigid masses with so many appendages—that the tips of the first pair 
of pleopods are thrust into the annulus. 
The two are now firmly united and cannot be readily separated, in 
fact it was found possible to kill and preserve them in this position, and 
thus obtain the photographs from which the illustrations are taken. 
When thrown into actively boiling water for a moment, the crayfish 
are fixed in the normal position with no observed change, and may then 
be preserved indefinitely. 
e firm union of the two is accomplished by the use of the hook- 
like spines that characterize the male of many species of Cambarus. 
In C. afnis there is one spine on the third segment, ischiopodite, of 
the third walking leg on each side of the body. When the male applies 
himself closely to the female, he fastens these two hooks to the base of 
her fourth walking legs, on each side. 
