CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 499 
that is to say, by sections made tangentially on the surface of 
the cone. Such sections are difficult to obtain exactly, but 
when they are in the direction wished for, they are very 
instructive. 
I represent four of these sections, which I shall describe 
successively, passing from the base to the free extremity. 
1. Section passing above the annular muscular layer (fig. 19) . 
We see the sensorial cell (a) in the middle of the reticulated 
connective tissue ( b ), in which we find also fibroid prolonga- 
tions (c) of the internal glandular cells. 
2. Section passing through the base of the epithelial group 
(fig. 20). Here we see the prolongation ( a ) of the sensorial 
cell, the continuation of the fibroid prolongations ( c ), and the 
surrounding connective tissue (6). 
3. Section passing through the extreme base of the epithe- 
lial cells (fig. 21). We find the rod (a) at the centre, with the 
refracting body ( b ), which is joined to it. All around are the 
bases of the central epethelial cells (e), in the interior of which 
we see the fibroid secretion ( d ) of the internal glandular cells. 
At the external part one sees connective tissue (e). 
4. Section passing through the epithelial cells (fig. 22). The 
external cells are already separated from their neighbours. 
We see in the middle the section of the rod (a), of which we 
distinguish the striated structure. In the membrane ( b ) of the 
epithelial cells we find some coloured points (c), indicating the 
sections of the longitudinal striae in this membrane, which I 
have already described. 
Summary. — What Eschricht has taken for suckers are 
epithelial cells terminated by a button-like enlargement. It 
is noticeable that there is no nucleus to be observed in these 
cells. Besides, they are penetrated by the secretion of the 
glandular cells which occupy the interior part of the cone. 
The latter are so numerous (apparently as numerous as the 
cells of the epithelial groups) that they doubtless fulfil im- 
portant functions. I think that their secretion is spread out- 
side of the cone across the button-like extremity of the 
epithelial cells, for on some specimens of which the epithelium 
