NOTES ON SOME AQUATIC OLIGOCHATA. 201 
circular section in all directions. Beddard,! in his figure of the 
sperm-duct of Hemitubifex, shows a different arrangement. 
The two parts of the atrium, already distinguished exter- 
nally, are equally distinct in histological structure: the non- 
glandular part (fig. 23, ngl. atr.) is lined by flat cells, with 
horizontally elongated nuclei and granular protoplasm ; whilst 
the glandular region (gl. atr.) is lined by cells of a totally 
different shape. The epithelium here is more or less cubical ; 
the cells are glandular—at any rate vacuolated, as if a secretion 
had been discharged; the protoplasm, with darkly staining 
granules of comparatively large size, is chiefly found in the 
outer part of the cell, where, too, is the round nucleus (fig. 
25); the spaces, or vacuoles, appear sometimes to be occupied 
by an extremely fine substance—so fine that it is impossible to 
detect whether it is homogeneous or finely granulated, and 
requires an apochromatic to be seen at all. 
The prostate is a solid structure, built up of a mass of 
cells having essentially the same structure as the preceding, 
though differing in shape (fig. 24). These cells are pyriform ; 
the granules are larger and distinctly spherical; probably the 
neck of each cell serves as a duct, and pours the secretion into 
the atrium independently of its neighbours. 
Mr. Beddard’s’ drawing differs slightly from mine, chiefly 
as to details, which is perhaps due to the method of preserva- 
tion. Ifthe cells in Heterocheta were a little emptier, we 
should have an appearance something similar to that shown 
by him for Hemitubifex. 
I may say that the isolated cells here figured are drawn from 
sections, and not from teased preparations. 
The prostate, like the sperm-duct and atrium, is sur- 
rounded by a delicate membrane (c. ep.), with a few scattered 
nuclei; this membrane is continuous, and is the celomic 
epithelium. The atrium has in addition a muscular coat, as 
shown in the figure (mus.). 
1 “On Certain Points in the Structure of Clitellio,” ‘Proc. Zool. Soc.,’ 
1889, p. 485, pl. xxili, fig. 5. 
? Loe. cit., fig. 7. 
