100 LIVERPOOL BIOLOGICAL SOCIETY. 
lum, and if so, in what manner are they connected ? 
To answer this question, some description of the epithe- 
lium is necessary. 
The epithelial tissues—There are three well marked 
varieties of the epithelial tissues to be observed in Crania ; 
these are :— 
(a) The epithelium of the body cavity generally, seen 
in the cavities of the arms, on the mesentery, and on 
the inner surface of the body-wall; it is squamous in 
character, and calls for no further comment. 
(b) The epithelium of the alimentary canal. In the 
anterior region it is very fine, deep, and with an undu- 
lating free margin. In the posterior region it is narrower, 
and approaches in character the columnar cells of the 
epidermis. It is continuous with the epithelium of the 
liver (which is nothing more than a follicular diverticulum 
of the alimentary canal). 
(c) The epidermis. This is columnar over the whole 
of the pallial chamber, that is on the inner surfaces of 
the mantle and over the arms. The cells are distinctly 
columnar throughout the whole area, but show certain 
modifications in particular regions. On the mantle, much 
of the body-wall, and those parts of the arms farthest 
removed from the fold and tentacles, it consists of short 
columnar cells with a distinct nucleus, the whole staining 
fairly well, but with a tendency to stain less deeply where 
attached to the sub-epithelial tissue. 
The epithelium is modified on the arms, over the whole 
of the sides of the tentacles and the fold which he next 
each other, and at the outer base of the fold, close to the 
large empty canal. In much of this area the epithelium 
differs simply from that of other areas by being deeper, the 
cells being long and rather narrow; but in the areas of 
special modification there is a groove in the sub-epithelial 
