1898-99. | THE MESENTERIAL FILAMENTS IN ZOANTHUS SOCIATUS. 395 
dermal. Is then the intermediate epithelium endodermal and diges- 
tive? This is a question difficult to answer, but it may be said that the 
epithelium is certainly continuous with the stomatodzeal ectoderm above 
and not with the endoderm. I do not find it essentially glandular in Z. 
soctatus ; indeed it contains relatively few gland cells in comparison 
with the epithelium of the median lobe. Those which do occur, how- 
ever, are very different from the usual stomatodzal glands with clear 
contents, since they stain deeply and are packed with granules. It is 
possible that such glands are digestive in function; they are especially 
abundant, as will be seen later, in the glandular streak of the filament, 
but they also occur here and there in the stomatodzal ectoderm and 
their occurrence in the intermediate epithelium cannot be accepted as evi- 
dence of its endodermal nature. From the evidence at my disposal [ am 
inclined to regard the intermediate epithelium as being ectodermal as is 
the rest of the ciliated band epithelium, and think it erroneous to homo- 
logize it with the digestive, or rather ingestive, area described by Willem 
which is unquestionably endodermal. I think, however, that intracellular 
digestion does occur in this epithelium, as I have seen imbedded in it 
particles which were neither Zooxanthellae nor normal constituents of 
the tissue, but which may have been ingested food particles. 
Il.—THE GLANDULAR STREAK. 
Following a series of sections downwards below the level represented 
in Fig. 2A we find the lamellz of the ciliated bands extending down- 
wards for some distance, but they finally disappear, the median lobe of 
the filament alone persisting. The general appearance of the glandular 
streak has been described and figured frequently, and reference may be 
made to the figures given by von Heider (1895), Haddon and Shackle- 
ton (1891) and myself (1889). The epithelium of this part of the filament 
forms a rounded or crescentic layer resting upon a somewhat T-shaped 
enlargement of the edge of the mesogloea. The tips of the crescent ex- 
tend to about the tips of the transverse limb of the T, the outer surface 
of the limb being covered by a very different kind of epithelium, gener- 
ally admitted to be endodermal. The general surface of the mesogloea 
of the mesentery, immediately external to the attachment of the T- 
shaped enlargement, is covered by a thick endodermal epithelium, which, 
traced outwards, gradually diminishes in thickness to pass into the ordi- 
nary epithelium of the mesentery. 
In Z. flos marinus | found (1889) in this thickened epithelium numer- 
ous foreign bodies and suggested that it was a special region for intra- 
cellular digestion. Haddon and Shackleton (1891@) have described the 
