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McMURRICH. 



[Vol. II. 



large oval nuclei situated about the middle of their length. At 

 the same time the large mucous gland cells disappear. Lower 

 still (at c in Fig. 5) the change is complete and an entirely 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 dis- 

 tinguish cilia in this region in my preparations, but am not 

 prepared to say that they do not exist. 



Following this stretch of tissue downwards, it is found to 

 change again to form the epithelium of the glandular streak 



Fig. 7. — Portion of 

 Fig. 5, about the 

 region b, more 

 higlily magnified. 



Fig. 8. — Portion of 

 Fig. 5, about the 

 region marked c, 

 more highly mag- 

 nified. 



Fig. 9. — Portion of Fig. 5, about the region 

 marked d, more highly magnified. 



(Fig. 9). This is very high again, higher even than that of the 

 stomatodaeum. It consists, like the latter, of supporting, sen- 

 sory, 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. sociatiis, but their absence is by no 

 means peculiar to that form. 



It is clear then that in Z. sociatus there is neither a histologi- 

 cal continuity nor a histological identity of the upper part of 

 the median streak of the filament with the lower or glandular 

 streak proper. The upper part is merely a continuation down- 

 wards of the stomatodaeal ectoderm, and this gives place to a 

 low epithelium destitute of gland cells and of a generally indif- 



