124 
FRANK E. BEDDARD. 
In Acanthodrilus, Pontodrilus, and Typhaeus the 
muscular layer of the atrium has been lost, and only a delicate 
peritoneal layer 1 remains ; otherwise the structure of the atrium 
is the same ; it is therefore probable that in all these forms 
(even Pontodrilus, which is now post-clitelline) the atria have 
been invaginated from the clitellar area. On the other hand, 
in Moniligaster the simple epithelium of the atrium may 
perhaps indicate that it has not been formed as an ingrowth 
from the clitellar area. This supposition is supported by the 
forward position of the atria in this worm. 
Professor Bourne has, however, lately (8, p. 662) described a 
species of Moniligaster where a clitellum is present in the 
neighbourhood of the male pores. 
I therefore make the above suggestion, which indicates a 
possible confirmation of Perrier’s classification of Earthworms, 
with considerable hesitation. 
In Pontodrilus the atria have acquired the character 
of an appendage of the vas deferens, and the penis is 
absent. 
In Typhaeus the independence of the atria and the vasa 
deferentia is more marked. The two organs appear to open 
on to the exterior of the body independently, but in reality 
they unite just below the epidermis. 
In Acanthodrilus the vasa deferentia open on to the 
exterior, quite independently of either of the two tubular 
glands of the seventeenth and nineteenth segments. 
In my paper on Acanthodrilus (1) I have wrongly 
stated that the two vasa deferentia of each side communicate 
with the two tubular glands. I have since found that in A. 
multiporus and A. dissimilis this is not the case. The 
vasa deferentia open on to the exterior on the eighteenth 
segment, close to the ventral pair of setae; they open by a 
single pore, and only unite just before the external pore. It 
is probable, therefore, that in Acanthodrilus generally there 
1 In Trigaster Benliam lias made the interesting observation (‘Quart. 
Journ. Micr. Sci.,’ vol. xxvii) that the muscular layer of the atria is partially 
retained. 
