404 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
The epithelial cells lining the ascending portion of 
the alimentary canal contain numerous granules like food 
granules, and the same green tint is present here also. 
It would seem from this that the pigment of the digestive 
gland is derived directly from the food taken into the 
alimentary canal. 
The rectum, after passing through the pericardium, 
continues its course over the adductor muscle under the 
connective tissue sheath. It does not run in the median 
line, but crosses towards the left side. At about the level 
where the circular muscles of the mantle edge are inserted 
to the shell the rectum leaves the adductor, and for its 
last centimetre is free. The anus is surrounded by a 
prominent lip. 
BLOOD SYSTEM. 
The blood system which has been worked out in 
Pecten maximus is very complete, and, like the vascular 
system of lamellibranchs in general, is entirely closed, so 
that water cannot enter the circulation directly. There 
is, moreover, no communication between the heart and 
the pericardial cavity, and this does not contain blood. 
The system comprises true vessels, mainly arteries, which 
are large and easily followed in injections, but the venous 
system is much more lacunary in character. The amount 
of blood is considerable, and when the adductor muscle 
has been cut, on opening the shell as much as 25 c.c. of 
blood have been obtained from one specimen. The blood 
is a colourless fluid shghtly thicker than water, with a 
strong saline taste. As is general for aquatic 
invertebrates, the osmotic concentration of the blood is 
practically the same as that of the sea water in which 
the specimen has been living, and small changes in the 
concentration of the outer medium are followed by the 
Oe eee eS ae ee Oe eS 
