S205 E. A. MINCHIN. 
Clathrinidz we see the contractile cells of the dermal 
epithelium migrating into the interior to become sclero- 
blasts, and probably returning again to the epithelium when 
this function is discharged. In the same way it is not 
difficult to imagine a cell which under certain circumstances 
becomes a pore-cell and under others becomes a gastral 
actinoblast, may under yet other conditions take on an excre- 
tory function. If Bidder’s term “ Metschnikoff’s cells” is to 
be used at all, I should suggest that it be used for cells such 
as I have described here, namely, cells of excretory function 
derived from the porocyte-layer, that is to say, from that 
part of the dermal epithelium which lines the oscular rim 
and furnishes the pore-cells and the gastral actinoblasts. 
And I may point out, that at a certain period in the develop- 
ment, or at any time during life in many Clathrinide, 
when they are contracted to a certain point, the porocyte- 
layer forms the innermost lining of the gastral cavity, ex- 
cluding even the collar-cells from it (1900, figs. 58, 4, and 
42, ¥F). 
The collar-cells of Leucosolenia complicata are shown 
in figs. 837 and 53; in other figures they are represented in 
outline. They are more or less flask-shaped, with the oval 
or pear-shaped nucleus at the upper extremity, close below 
the collar. The flagellum can be traced down to the 
nucleus. The collar is long and cylindrical; its free rim is 
difficult to make out. About half-way up the collar shows a 
hoop-like thickening. The cytoplasm is clear and finely 
granular, occasionally with a few coarser refringent granules 
and usually distinctly vacuolated. In sections it is common 
to find a collar-cell cut in such a way that only the base is 
shown. I have drawn one cut in this way in fig. 56 (ce. ¢.) in 
order to show the difference between it and an excretory cell 
(Gis C))c 
A cytological study of the collar-cell, its nucleus, and the 
mode of division would be of great interest. Unfortunately 
the osmic-picrocarmine method used by me, though very good 
for cytoplasmic details, gives very poor results for nuclear 
