OLIGOCHZTA OF TROPICAL EASTERN AFRICA. 263 
logically identical, but morphologicallly different). The princi- 
pal feature of interest in the anatomy of the Eudrilide is the 
presence of coelomic sacs which do duty as spermatothece. I 
have called these sacs consistently “‘ spermatothecal sacs” to 
mark their difference in structure from, but their similarity in 
function to, the spermatothecee of other Oligocheta. Michael- 
sen, it is true, has denied to the spermatothecal sac of the 
Eudrilide the function of storing sperm. They have, however, 
been proved to contain sperm in Nemertodrilus, Eudrilus, 
and Polytoreutus. That these sacs are not homologous 
with the spermatothece of other Oligochzta is shown by their 
development. I have pointed out that in Libyodrilus the 
sac is formed at the expense of the septa, and Rosa has 
arrived at the same conclusion by a consideration of the 
histological structure of the sacin Paradrilus. Thereis, how- 
ever, at least one genus in which the spermatotheca appears 
to be of the type general in the Oligocheta. In Heliodrilus 
there is a single long and narrow sac which opens externally 
on to the 11th segment, and reaches back to the 18th. At 
the extreme end the spermatotheca is enclosed by a ccelomic 
sac continuous with the ovarian sac, &c. I have no facts 
of development to offer in support of my belief that the 
spermatotheca in this Annelid is comparable in origin to that 
of other earthworms ; I rely upon its structure and relations. 
The sac in question is lined by a columnar epithelium, quite 
different in appearance from the cells which line the sac 
in which it lies, but quite like the cells which are found in the 
spermatothece of other worms, in which these organs are 
epidermic invaginations. This is, I hope, plainly shown in 
the figures illustrating my account of the anatomy of Helio- 
drilus. The next stage is seenin Hyperiodrilus. Here 
we have the true spermatotheca reduced to very small dimen- 
sions, and the sac involving it is greatly increased in size. In 
Paradrilus it is possible, whether it actually occurs or not, 
for sperm to reach the interior of the large celomic sac; for 
this sac communicates directly with the exterior by a short 
tube which seems to be an invagination of the epidermis, and 
