CONTRIBUTIONS TO THE ANATOMY OF EARTHWORMS. 423 
The nephridiopores open in front of the lower seta of the 
dorsal pair ; these orifices were particularly obvious upon the 
clitellar segments. 
The apertures of the atria are upon segments xvii and 
xIx, and correspond to the ventral sete, which are here 
modified and form special penial setze, as in all other species 
of Acanthodrilus; these apertures are surrounded by a 
ridge, and a narrow groove connects the two apertures of 
each side of the body ; this no doubt enables the secretion of 
the atria to mingle with the sperm, which is discharged from 
the orifice of the vasa deferentia upon the eighteenth segment 
within the said groove. 
The oviducal pores were not visible. 
Alimentary Tract.—Dr. Michaelsen mentions that in A. 
georgianus there is a dorsally-placed diverticulum of the gut 
in the fifth segment. Ifthis refers to a diverticulum of the 
pharynx, then I can confirm him, and state also that other 
species of the genus agree with A. georgianus; this diverti- 
culum can be plainly made out from a series of transverse sec- 
tions. In the Oligocheta generally the dorsal wall of the 
pharynx is specially thickened, while in other Annelids, e. g. 
embryo Serpula, the ventral wall is thickened, and forms a 
diverticulum (see Weldon, 41). It does not appear to be novel 
for the dorsal wall of the pharynx to form a diverticulum, as 
is often the case in Acanthodrilus; but in Acolosoma 
tenebrarum (Vejdovsky, 39) the pharynx is furnished with 
two minute diverticula, which probably correspond to the 
unpaired diverticulum of Acanthodrilus georgianus. It 
is interesting to note that the dorsal position of the pharynx 
in the Oligocheta, and of the diverticulum where such is 
present, contrasts with its ventral position in Polycheta. 
A. georgianus does not possess a well-developed gizzard. 
In the fifth segment the muscular walls of the cesophagus 
become thickened, but the chitinous lining of this part of the 
gut is thinner than the external chitin; but the proportion of 
the muscular coat and the lining epithelium (see fig. 38) are 
very much less than in other worms which have a well- 
