Sete 
a 
938 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
prominent otolith, marked with concentric and radiating 
lines, exactly spherical in form, and about 0°02 mm. in 
diameter, is present. The wall of the otocyst is composed 
of a single, rather irregular, layer of cells; at the extremities 
of the long diameter are two single, nucleated cells, the 
cell bodies of which stain deeply, and on either side of 
each of these are several clear, apparently non-nucleated, 
spindle cells. The remainder of the wall is composed of 
irregular cubical cells. Hairs or cilia are not clearly 
shown. The nerves seem to enter at the internal poles 
of the organs. Each otocyst is surrounded by a loose 
investment of fibrous connective tissue, and but for this, 
hes freely among the transverse muscles of the foot. 
THE REPRODUCTIVE ORGANS. 
The gonad is paired and consists of a branching tubular 
gland. The external opening (see fig. 3, Pl. I.) is situated 
on the lateral and posterior body-wall, near the origin of 
the posterior retractor muscle of the foot. This leads into 
a very short terminal duct which immediately branches 
into three main divisions (fig. 3). One of these runs 
dorsally along the posterior margin of the viscero-pedal 
mass, the second downwards along the body-wall, the 
third duct runs obliquely forwards and downwards towards 
the bend of the foot. Branches are given off laterally 
from all these ducts on which are borne botryoidal clusters 
of secreting alveoli (fig. 37, Pl. VI.). These lateral 
branches penetrate among the transverse muscle bundles, 
between the convolutions of the intestine and between 
the lobes of the digestive gland. They he principally 
in the peripheral zone of the proximal limb of the viscero- 
pedal mass. There is no extension at any time into the 
distal limb of the latter, nor into the mantle lobes. 
In Cardiwm edule the sexes are separate, In at least 
