The Morphology of Coeloplana. 49 
organs would appear to be respiratory and this view is supported 
by the fact that the tentacles are seldom if ever protruded except 
when the water is a trifle stale. They do not seem to have any 
sensory function, as they may be touched or pushed aside with a 
needle without being withdrawn or causing any reaction in any 
other part of the animal. The tentacles themselves, in C. willeyi, 
are colorless but the epithelium at the base is heavily pigmented. 
In ©. mitsukurv, on the other hand the fringed tentacles are densely 
pigmented and are hardly to be distinguished from incrusting debris. 
2. Structure of Coeloplana. 
a) Epithelium. 
Compared with the ordinary Ctenophores, the epithelium of 
Coeloplana is relatively firm and well developed. There are at least 
four well marked cell elements in its makeup. 1) Gland cells, 
2) Interstitial cells or interstitial syncytium, 3) Supporting (ciliated) 
cells, 4) Pigment cells. 
Gland cells occur in great numbers all over the body, but are 
especially numerous at the periphery. They are fewest in number 
and smallest in the region directly over the tentacle sheathes, — 
where the epithelium is also relatively much thinner. The various 
stages in the development of the gland cells, as worked out by 
Samassa are well represented in Coeloplana. The clear fluid 
contents of the cells becomes divided off into globules by thin sheets 
or trabeculae of differentiated cytoplasm, which increase in number 
and in size until the cell is gradually filled with an anastomosing 
network of fibrils that stain intensely in haemotoxylin and other 
basic dyes (Samassa’s Stage B). The fluid contents of the inter- 
trabecular spaces does not stain with either acid or basic dyes, — 
at least not by any method tried so far. But at a certain point a 
sudden chemical and physical change intervenes and the staining 
reactions are reversed. The formerly fluid globules appear to gel 
or coagulate and stain intensely with eosine or other acid dyes, 
while the formerly very evident network either disappears or re- 
fuses to take any stain. This is the “Stage C” of Samassa. In any 
one preparation the majority of the gland cells will usually be found 
in either Stage B or Stage C, but in a very few instances I have 
found indications of the cell having been killed during the change 
Zool. Jabrb. XXIV. Abt. f. Anat. 4 
