STRUCTURE OF THREE NEW SPECIES OF EARTHWORMS. 127 
one of those described by Fletcher (11)., the prostate glands 
(PL XIII, fig. 15) have a tubular form like those of Acan- 
thodrilus; this fact is also noted by Fletcher. I find, 
however, that these glands are really branched like those of 
other Perichetae (PI. XIII, fig. 13), but there is only a faint 
indication of the division of the gland into lobules. The 
structure of the gland in this species is therefore intermediate 
between the ordinary Perichetae and Acanthodrilus, &c. 
It has been said that the structure of the atrium in Acantho- 
drilus is identical with that of the corresponding organ in 
Perichaeta, allowing only for the branched character of 
the supposed atrium in Perichaeta. In Perichaeta, how- 
ever, the lining epithelium (PL XIII, fig. 13) is distinctly 
columnar and not glandular ; it is very sharply marked off 
from the surrounding glandular layers. In Acanthodrilus 
(PL XIII, fig. 14) and Deinodrilus (PL XIII, fig. 16) 
the lining epithelium is loaded with granules, and is on that 
account rather difficult to distinguish from the glandular 
layers surrounding it; in any case, this difference does not 
appear to me to be one of importance; but if it were then 
Pontodrilus could hardly be referred to either category. The 
layers of cells which form the atrium (PL XIII, fig. 12) are 
like those of Perichaeta in the obvious difference between the 
innermost layer of cells and those which surround them ; 
the cavity of the atrium is, however, unbranched like that 
of Acanthodrilus. This series of facts leads me to 
believe that the so-called prostates of Perichaeta 
are equivalent to the atria of Acanthodrilus and 
Pontodrilus, &c. 
In Criodrilus Rosa (17) has recorded the presence of a 
gland surrounding the external orifice of the vas deferens. 
This he has termed the atrium. The investigations of Benham 
have shown that this supposed atrium is nothing more than a 
group of cells continuous with the clitellum. I have found 
the same thing in Allurus. 
The vas deferens passes through the glandular body and 
opens on to the exterior ; it undergoes no changes in its 
