426 FRANK E. BEDDARD. 
The vasa deferentia are described by Michaelsen as 
opening on to the exterior on the seventeenth and nine- 
teenth segments, in common with “the large, lobulated 
prostates.” 
I find that in this, as in other species of the genus, the vasa 
deferentia open at the eighteenth segment quite independently 
of the atria, with which they have no connection. A species of 
Acanthodrilus has recently been described (20) from Illinois, 
U.S.A., under the name of Diplocardia communis; one of 
the principal structural characteristics of the species, which led 
the author to infer it to be a distinct genus, is the independent 
opening of the vasa deferentia on to the segment lying between 
those upon which the atria open; but this is no generic dis- 
tinction, neither is the completely double condition of the 
dorsal vessel, which Mr. Garman also uses as a differential 
character, distinguishing Diplocardia from Acantho- 
drilus. The atria of A. georgianus, like those of other 
species, are tubular, not lobate; their minute structure, as well 
as their general anatomy, is precisely that of A. dissimilis and 
other species. 
The sperm-sacs of A. georgianus are very remarkable ; 
there are in the first place a pair of racemose organs attached 
to the front walls of segments x1 and x11; these resemble the 
sperm-sacs of A. dissimilis, &c. (see Beddard, 1, where 
they are, however, spoken of as testes), and were full of 
developing spermatozoa. In the ninth to the fifteenth segments 
inclusive is a median unpaired sac lying under the wsophagus 
and above the supraneural blood-vessel. This sac appears to 
be interrupted at the septa; its walls are very thin and appear 
to be muscular, with a coating of peritoneum (fig. 35). This 
structure recalls the unpaired sperm-sac of the Tubificide and 
other ‘‘ Limicole” by its position and great extent, but I am 
unable to be certain whether it represents such a structure, at 
any rate physiologically, as there were hardly any developing 
spermatozoa within it; the few “sperm-polyplasts” that 
could be observed may have got there accidentally. The de- 
velopment of the sperm-sacs in the Oligocheta is but little 
