THE COCKLE. 57 
bends downward and passes gradually into the intes- 
tine. The intestine, after one or two convolutions, 
ascends to the dorsal side and passes straight to the 
dorsal siphon. Remove the stomach, place it on a slide, 
and gently press it down with a glass cover. Examine 
with the inch objective. Notice the crystal style, a 
long transparent bristle-like organ, tapering to one 
end and rounded at the other, and curved toward the 
thin end. This is not always present. Its function 
is unknown. Cut out the rectum and examine. On 
the under side between where the heart was situated 
and the anus, there is a solid hemispherical projection, 
the function of which I do not know. 
10. The shell—Remove the animal and examine the shell. 
The interior. Notice the three diverging teeth on 
the hinge, which interlock with the teeth on the 
other valve when the shell is closed; the impres- 
sions made by the attachments of the two adductor 
muscles ; the line made by the attachment of the 
muscles of the mantle to the shell—the pallial line. 
This line leads from the anterior adductor impression 
round the ventral side of the shell, and forms a deep 
re-entering angle before reaching the impression of 
the posterior adductor. This is the pallial sinus. 
The exterior. The wmbo is the pointed portion of the 
shell, above the hinge, which curves forward; below it. 
on the anterior side is the lunule. Behind the umbo is. 
the black projecting horny ligament, which by its elas-. 
ticity opens the valves when the adductor muscles. 
are relaxed. The shell is radiately ribbed with 
rounded ribs, which start from the umbo, and these: 
ribs are crossed by rather sharp concentric lamine,. 
which mark old lines of growth of the shell. 
