454 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
since the anatomy of the annulus favors the idea that a compressing 
force exerted from behind forwards might make the zigzag suture 
(pi. 43, fig. 1, and text-figure B) spring open, especially at its angles. 
There still remains the possibility that the glaire secreted by the 
female may play some part in discharging the sperm from the annulus; 
possibly it may penetrate into the orifice and cause an expansion of 
the contents of the trumpet; but the mechanical pressure in actual* 
experiments was the only factor necessary, unless the egg albumen 
played a part. 
The recess commonly remains full after the tube is emptied though 
it may be emptied at the same time (pi. 43, fig. 10). This behavior 
of the recess might be explained upon the hypothesis that the penetra¬ 
tion of glaire was necessary to discharge it, for it was noticeable that 
in staining annuli the recess remained very long unstained, and again 
when finally stained, was very slowly decolorized so that the accessi¬ 
bility of the contents of the recess to liquids from without is much 
less than that of the contents of the trumpet tube and thus the recess 
would long remain unaffected by glaire. On the other hand mechan¬ 
ical pressure alone may conceivably sometimes discharge the recess 
and the common failure to discharge is what we would expect unless 
the pressure were very great. For from figure 14 (pi. 44) and the 
series of sections (pi. 43, fig. 8; pi. 45, fig. 16), it is evident that the 
recess is too firmly embedded in the thick exoskeleton to be readily 
compressed and, moreover, its connection with the exterior is so 
indirect and restricted that discharge Avould seem more difficult than 
from the trumpet tube. 
In conclusion, we seem justified in supposing that mechanical 
pressure furnished by the female is the cause of the cracking open of 
the annulus and of the squeezing out of sperm which then spreads by 
surface tension. However, the possibility that the secreted glaire may 
take part in the emergence of the sperm or even in the opening of the 
suture, is not absolutely excluded. 
Structure in Cambarus virilis .— To determine if the use and struc¬ 
ture of the annulus described in C. affinis was peculiar to this species 
or common to all the genus, a few other species were selected at ran¬ 
dom and studied sufficiently to indicate that the latter alternative is 
the probable one. In Cambarus virilis brought here from Chicago 
markets, several cases of pairing were observed in October and Novem¬ 
ber and the habits of the male seem to be essentially the same as in C. 
affinis (Andrews, : 04 ). 
