SEA-FISHERIES LABORATORY. A038 
ventricle of the heart. Here, as in many other lamelli- 
branchs, we must assume that the ventricle has grown 
up around the alimentary canal, so that the wall of the 
heart lies between its cavity and the walls of the 
alimentary canal. Outside the usual lining epithelium 
there is a basement membrane of connective tissue with 
a few circular muscle fibres, and external to that a thick 
sheath of looser connective tissue. The epithelial cells 
(fig. 44) resemble in appearance those of the ascending 
limb of the intestine. They are deep columnar cells, the 
height being many times the diameter, and the cilia are 
rather poorly developed. The ends of the cells facing the 
cavity have a strange appearance, as if either a part or the 
whole cell were being shed into the lumen of the intestine. 
These shed cells seem to have no stainable contents and 
no signs of nucleus, and when cut off completely appear 
in the intestine as spherical bodies faintly stained but 
with a very definite wall. Lying scattered amidst the 
connective tissue surrounding the intestine, especially in 
that part passing through the pericardium, are 
conspicuous wandering cells, pear-shaped, with most of 
the protoplasm and the nucleus at the narrow end, and a 
very large vacuole taking up practically the whole of the 
rest of the cell. There is generally a large mass of dark 
yellowish green material in this vacuole, which renders 
these cells very obvious. The same cells are found in 
considerable numbers, and carrying the same pigmented 
contents, in the connective tissue of the digestive gland. 
It is impossible, however, to say whether their function 
is excretory or nutritious, and whether the coloured 
contents are extruded by the cells lining the ahmentary 
eanal or not, but they resemble so closely those of the 
pericardial gland on the auricles, which are excretory, 
that they are presumably the same. 
