ANDREWS: ANNULUS VENTRALIS. 
443 
say, right-handed, there were also left-handed specimens. In these 
the symmetry of the annulus was exactly reversed (pi. 43, fig. 10; 
pi. 47, fig. 28). Comparing figures 5 (pi. 43) and 28 (pi. 47) we see 
that each is the mirror-image of the other. They also show individ¬ 
ual differences in proportion and angle. In the left-handed annulus 
the orifice is on the left of the animal and the right tuberosity sends 
a spur across toward the left tuberosity while the zigzag and the curved 
slits as well as the bends of the trumpet, are all the reverse of what 
they are in the right-handed annulus. 
Both right- and left-handed annuli were used as sperm receptacles 
and no difference in use w r as discovered. 
Use of the annulus in Cambarus affinis .—As the annulus is 
mainly an external pocket of dense calcified exoskeleton, its use 
as a sperm receptacle would seem a 'priori improbable, and the 
important questions as to how the sperm is put into it, how it is kept 
there uninjured, and how it is finally got out and applied to the eggs, 
all demand consideration. 
Proof that the annulus is indeed a physiologically necessary part 
of the reproductive system rests upon a number of observations and 
experiments. 
The way in which sperm is put into the cavity of the trumpets of 
the annulus in C. affinis is, in brief, as follow’s. As seen in captivity, 
the males eagerly seize the females, from October to the early part 
of April, and by a complex series of adjustments, elsewhere described 
(Andrews, : 04 ) finally fill the tube of the trumpet and the recess with 
sperm. During this long period females usually have the recess and 
the tubule of the trumpet full of sperm, while the vestibule is packed 
with a wax-like mass that protrudes from the orifice (pi. 47, fig. 28) 
and witnesses to the union with the male. But in the summer the 
females have little or no sperm in the annulus, at most a little in 
the recess. 
The eggs are laid in March or early in April, and in cases under 
observation some weeks intervene between the reception of sperm and 
the laying of eggs, a period in which the female keeps away from the 
male and begins remarkable preparation for laying. This period in 
which the sperm, though carried about by the female, has not got 
access to the eggs is often much greater and may extend through the 
entire winter. 
In actual isolation experiments, females kept isolated entirely for 
