2972:)] J. StEPHENSON : Indian Aquatic Oligochaeta. 225 
The buccal cavity is tubular, and is succeeded by the pharynx, 
a portion of the tube which possesses a strongly ciliated and 
laterally extended dorsal diverticulum, the cells lining which are 
markedly columnar; while the ventral wall of the pharynx is 
composed of flatter and more irregular cells (pl. xi, fig. 5). The 
pharynx extends backwards to include the first gilled segment ; 
the diverticulum then flattens out and disappears. The oesophagus 
is strongly ciliated; there is no stomach,—indeed, beyond the 
pharynx, the tube can scarcely be differentiated into distinct 
regions. 
The dorsal vessel is, for by far the greater part of its extent, 
dorsal in name only; it runs for the most part on the left of the 
intestine (pl. xi, figs. 2, 6) ; it is invested by chloragogen cells and 
pigment cells as far forward as the interval between first and 
second gills ; here it becomes dorsal, and loses its investment. 
The present species does not stand alone in the matter of the 
aberrant course of the dorsal vessel. I have ascertained, from an 
examination of my specimens, that B. hortensis is similar in this 
respect, though the fact was not noted in my original account of 
this worm. It is known also to be the case in the various species 
of the genus Dero (Naididae), and in Branchiura sowerbyi 
(Tubificidae) (1, 13) ;and I have found it alsoin the Tubificid worm I 
have described (13) as Limmnodrilus socialis. One peculiarity common 
to all these forms is that they possess specialized respiratory arrange- 
ments ;—Devo, Branchiura, and Branchiodritus possess branchiae, 
while Limnodrilus socialts has a well-developed integumentary blood 
plexus in the posterior part of its body, and during life is inces- 
santly waving this posterior end in the water; but as to what 
connection there is between such specialized respiratory arrange- 
ments and a lateral or ventrolateral position of the dorsal vessel 
I am not clear. 
There is a large giant fibre on the dorsal surface of the ventral 
cord, looking in sections like a large empty tube (pl. xi, fig. 6). 
(2) Asexual Reproduction. 
One specimen only was dividing asexually (pl. xi, fig. 4); and 
here a fragment only of the posterior animal was present. ‘The 
whole specimen consists of 87 segments in the anterior animal, and 
nine segments of the posterior. Though apparently nearly ready 
for detachment, there is as yet no differentiation of a head in the 
hinder zooid, no mouth, and no new setae, no newly formed 
segments, nor any region intervening between the first gilled 
segment and the anterior end of the body ; the gills however have 
formed, and the characteristic pigmentation of the anterior region 
is beginning to appear. At the posterior end of the anterior 
animal there is an appearance suggestive of the approaching rapid 
formation of a budding zone,—a slight opacity, and an irregular 
fine transverse streaking, more especially on the ventral half 
of the body. 
