428 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
organs used in eases of indirect sperm transfer. That is, one of those 
exceptional cases met with here and there in several of the large groups 
of animals, in which the sperm is neither set free in water nor trans¬ 
ferred into the egg-discharging passages by an intromittent organ. 
In the following pages the anatomy and use of the annulus will be 
described more in detail than has been done hitherto though a pre¬ 
liminary account was published elsewhere (Andrews, : 05 ). 
Description. 
Structure in Cambarus afjinis .— Externally the annulus ventralis 
appears as a part of the shell, or exoskeleton, on the ventral side of 
the female thorax. It is a transversely elongated, elliptical plate, 
lying across the middle of the body in the interval between the two 
special sternal plates that lie between the bases of the fourth pair of 
legs and between the bases of the fifth pair of legs. 
In text-figure A the bases of the 2, 3, 4, and 5 pairs of legs with the 
sternal plates between 
them are shown and also 
the small first pair of 
abdominal appendages. 
On the bases of the third 
legs are the two large 
elliptical openings of the 
oviducts; posterior to 
these the wide, concave 
sternal plate between the 
bases of the fourth legs; 
and crowded close against 
this is the annulus bear¬ 
ing two marked protuber¬ 
ances and a deep trans¬ 
verse depression bounded 
posteriorly by an elevated 
Fig. A. rim. Posterior to the an¬ 
nulus, the narrow sternum 
between the fifth legs bears an elevated transverse ridge that will 
subsequently be referred to in attempting to explain the way in which 
the sperm is discharged from the cavity of the annulus. 
