Hirudinea. 
163 
her of annuli, the one further removed from the middle exhibits always a condition 
approaching the next stage of reduction. For instance, of the somites IV and V the 
latter is more decidedly biannulate, whereas in IV the furrow separating the annuli 
is rather faintly developed. VIII and X have likewise one annulus less on the ventral 
side, the first and second being fused here except at the margins Our leech shows, 
thus, a perfect series of gradations between the uniannulate condition at the extremities 
and the typical quinqueannulate somites in the middle part of the body. 
There are five pairs of eyes situated exactly like those of Hiritdo or Haemopis, i.e. 
a pair each on the 2nd, 3rd, 4th, 6th and 9th ring. The second pair is the largest. 
They all lie rather deep beneath the surface, so that they could be detected only after 
clarifying in oil. 
The configuration of the oral sucker is somewhat peculiar (pi. vii, fig. 3). It is a 
small cup-shaped deepening on the ventral side of the head, and is bounded poste- 
riorly by a double ring corresponding to the 6th and 7th annuli on the dorsal sur- 
face. From the bottom of this deepening, near its posterior end, is seen projecting a 
.short papilla-like elevation, upon the summit of which the tiny mouth-opening is 
.situated. In preserved specimens this structure is more or less flattened and looks 
somewhat like a miniature tongue. The mouth itself is distinctly three-rayed, being 
composed of a dorso-median and two ventro-lateral slits meeting at the centre. As 
there is no Gnathobdellid in which the oral sucker shows such a structure, it would 
be very interesting to investigate the use of this organ in life. Possibly it might rep- 
resent a sucking apparatus in primitive condition, which, when further developed, 
would lead to the formation of the tubular proboscis so characteristic of the Rhyn- 
chobdellida. 
The genital openings correspond in position exactly to those of Hirudo, i.e. the 
male opening lies between the 4th and 5th rings of somite XI, and the female be- 
tween the 4th and 5th rings of somite XII. They are both quite inconspicuous, 
there being no special elevation or glandular area to indicate their position. In all 
three of Dr. Annandale's specimens the clitelium was not developed, although they 
were all mature as judged from the condition of the genital glands of one dissected. 
One of Prof. Earle's specimens showed it tolerably well; it extends, as in Hirudo, 
from the third ring of somite X to the second ring of somite XIII, both inclusive. 
The nephridial pores could not be detected externally in Dr. Annandale's speci- 
mens, but in some of Prof. Earle's examples the position of these opening was indi- 
cated by the local widenings of the furrows containing them. There are in all seven- 
teen pairs, as in Hirudo, the pores being situated in the furrow separating the 2nd 
and 3rd rings of somites VIII — XXIV. 
The posterior sucker is attached to the ventral side of somites XXII-XXVII. 
The anus is located on the dorsal surface of the sucker in a slight transverse furrow 
just behind the last annulus of the trimk. 
It is very interesting to notice that in our leech the furrows separating the annuli 
of a typical somite are not of equal depth, as in all other genera, but form a regular 
set of four different depths. The deepest furrow is always the one separating the 
