OLIGOCHATA OF TROPICAL EASTERN AFRICA. 227 
Opening into the atrium. The atria lie perfectly straight on 
each side of the body ; they are comparatively short, and are 
not twisted as is so frequently the case with the longer atria of 
other species. Each atrium consists of two parts; the external 
pore leads into a nearly spherical and very muscular bulbus ; 
from this arises the atrium proper. This tube is quite as wide 
as the terminal bulbus, and has a nacreous appearance. This 
appearance is of course due to the stout muscular walls of the 
organ. In longitudinal sections the atrium is seen to be com- 
posed of four layers exclusive of the peritoneum ; beneath the 
peritoneum is a layer of longitudinally disposed fibres ; beneath 
this, again, a layer of circular fibres. These two layers are of 
about the same diameter. The iining membrane of the atrium 
is built up of two strata of epithelium ; the innermost layer is 
composed of not very tall columnar cells, outside which are 
several layers of slightly staining pear-shaped glandular cells. 
The two layers of epithelium together are twice as thick as the 
muscular coats. 
Kach atrium is accompanied by a long, thin, muscular sac, 
which is nearly, if not quite, as long as the atrium itself. This 
sac is placed to the outside of the atrium, and is slightly 
curbed. Each of the two sacs contains a single very long 
penial seta, It is very thin, and curved more sharply at the 
free extremity. The free end of the seta expands at the actual 
extremity into a thin, flattened plate; just before this the seta 
is beset with a few short spinelets. 
I have been able to study the female reproductive system in 
immature worms, and to ascertain that the spermatothecal 
apparatus is formed from at least two sources. The sper- 
matotheca appears to be formed by an epidermic invagina- 
tion. Its lining epithelium is continuous with the epidermis. 
This sac is large and has very thick walls. It appears at 
first sight to be independent of any other part of the system 
and I believe that originally it is so. However, in all the 
specimens examined by me there is a strand of tissue, princi- 
pally constructed of muscular fibres, which has in the imme- 
diate neighbourhood of the spermatotheca no lumen, This 
