1898-99. | THE MESENTERIAL FILAMENTS IN ZOANTHUS SOCIATUS. 397 
with granular contents are, on the contrary, rather rare. In addition, 
some darkly staining, slender, probably sensory, cells occur, the rest of 
the tissue being composed of ciliated cells which stain only moderately 
and are probably supportive cells. As I have already stated, the 
median epithelium of the ciliated bands is continuous with this above 
and is histologically identical with it. Tracing the section downwards, 
however, it will be found that the median epithelium gradually becomes 
lower, and, at a certain region, it changes somewhat abruptly its histo- 
logical character. 
Fig. 7 represents a portion of the epithelium at the region where the 
change takes place (6 in Fig. 5). The upper part of the portion fig- 
ured is essentially the same as the stomatodzal ectoderm, but in its 
lower part there appear cells which stain somewhat darker than the or- 
dinary supporting cells and have large oval nuclei situated about the 
middle of their length. At the same time. the large mucous gland cells 
disappear. Lower still (¢ in Fig. 5) the change is complete and an en- 
tirely new form of epithelium occurs (Fig. 8). In this the cells are still 
lower, they contain large oval nuclei arranged in about two or three 
layers at the middle part of the epithelium, and there is apparently an 
entire absence of gland cells. I could not distinguish cilia in this region 
in my preparations, but am not prepared to say that they do not exist. 
Fic. 7.—Portion of Fig. Fic. 8,—Portion of Fig. 5 Fic. g.—Portion of Fig. 5 about 
5 about the region 4, more about the region c, more the region d, more highly magni- 
highly magnified. highly magnified. fied. 
Following this stretch of tissue downward it is found to change again 
to form the epithelium of the glandular streak (Fig. 9). This is very 
high again, higher even than that of the stomatodzum. It consists, like 
the latter, of supporting, sensory and gland cells, but the gland cells are 
all of the kind with granular contents. I have found no nematocysts in 
the glandular streak of Z: soctatus, but their absence is by no means 
peculiar to that form. . 
