166 bulletin: museum of comparative zoology. 



between adjacent vacuoles which form a single superficial layer and are 

 by pressure elongated in the long axis of the cell. In Figure 7 some 

 cells exhibit large globular protrusions from their free ends. The cj'to- 

 plasm of these protrusions is less dense than that at the base of the cell, 

 and they bear some resemblance to the globules found on the cells of the 

 endsac. Other cells in Figure 7 show two or three small globules, and 

 still other cells might have been shown having a larger number of pro- 

 portionally smaller globules. I believe that the large globules arise from 

 cells in the condition seen in Figure 8, by the progressive fusion of neigh- 

 boring small vacuoles at the free ends of the cells, accompanied by an 

 expansion and protrusion of the wall of the free end of the cell. As far 

 as my observations go, I can agree with the main points of Marchal's 

 ('92, pp. 228-230) description of this process, except that I do not find 

 secondary smaller globules within the larger ones. 



The large terminal globules evidently become detached from the cells, 

 since great numbers of such globules (Fig. 7, gib.) of various sizes ap- 

 pear free in the lumina of the tubules. They resemble the globules from 

 the endsac in being spherical, but their contents are much more homo- 

 geneous, the granules being nearly alike in size and refractive properties. 

 This production of globular bodies with granular contents characterizes 

 the cells of both endsac and labyrinth, but the manner of their formation 

 differs somewhat in the two cases. There is, then, a tj'pical true secre- 

 tion by these cells, not merely a filtration of substance through them. 



The vesicle has a wall without folds or protuberances. It is com- 

 posed of tliree layers; the inner one epithelial (Plate 1, Figs. 10 and 

 11, la. e'th.), the outer one muscular (la. mu.), and between these a third 

 layer containing a system of blood vessels (Figure 11). 



The epithelium is throughout one laj'er deep. The cells in surface 

 view (Fig. 9) are seen to be irregularly polygonal. They are often elon- 

 gated parallel to the axis of an underlying blood vessel. The resemblance 

 to the cells of the labyrinth is close, as is to be expected from their sim- 

 ilarity of origin (p. 189). The cytoplasm is granular and striate, but 

 shows more vacuoles (Figs. 9, 10, and 11) than occur in the cells of the 

 labyrinth. The nuclei are oval and situated near the middle of the cell. 

 There is a basement membrane of appreciable thickness, which may be 

 separated from the cells by maceration and teasing. The free border of 

 the epithelium (Figs. 10 and 11) presents the same condition as that seen 

 in Figure 8 from the labyrinth ; but I do not find the other extreme condi- 

 tion (Fig. 7), with large globules attached to cells, although some of the 

 earlier intermediate conditions between these two extremes are found. 



