OLIGOCHAHTA OF TROPICAL EASTERN AFRICA. 211 
of the pouch is encircled by a cup-shaped layer of epithelium 
whose cells are of an altogether different character. These cells 
are regular columnar cells with the nucleus at about the 
middle. They have every appearance of being epidermic cells 
invaginated, but I could not find that they were at any point 
continuous with the epidermis; there was a slight break on 
either side. This, however, is not fatal to the view that they 
are invaginated epidermic cells. These cells, so easily dis- 
tinguishable by their characters from the thick mass of cells 
occupying the inner surface of the spermatothecal sac, do not 
immediately abut upon the latter; the two layers are separated 
by a thick, non-staining membrane which has every appear- 
ance of being of a chitinous nature; it is homogeneous and of 
a faint horn colour; it completely divides the two layers of 
cells spoken of. This species has, like Eudriloides brun- 
neus, glands at the sides of the spermatothecal sac (see 
fig. 19). These have, apparently, precisely the same structure 
as in that species, and need not therefore be particularly de- 
scribed ; there is, however, but a single pair of them. The 
ducts of these glands open partly on the exterior direct, and 
partly through the layer of cells already spoken of and pre- 
sumed to be formed by an invagination of the epidermis. 
This is additional evidence of the justice of this interpretation 
of the cells in question. 
In a younger specimen of the species the spermatothecal sac 
was less fully developed ; the posterior part of the sac is very 
thin-walled, and lies to one side of the nerve-cord ; it looks like 
a piece of a septum detached, and has a roughly circular con- 
tour. Following the course of the sac in a series of sections, it 
is seen to get beneath the nerve-cord and to lose its lumen; at 
the same time it decreases in diameter ; at the external aperture 
there is a protuberance of the body-wall in which there is a 
slit-like crescentic lumen bordered by tall columnar cells; a 
lumen also suddenly appears in the dorsal part of the sac which 
is quite independent of the crescentic lumen referred to; this, 
indeed, is merely the border line between the tall columnar 
cells, which I believe to be an invagination of the epidermis, 
