l62 
ZOOLOGY OF THE FAR EAST. 
The thickness of the body at the thickest part is 4-5 mm. The posterior sucker is 
circular in outline, about 6 mm. in diameter, and not very deep; it is connected with 
the trunk much in the same way as in the ordinary medicinal leech. 
External Characters. Undoubtedly the most conspicuous of the external features 
of this leech is that the body is divided by deep furrows into distinctly bounded 
somites, each of which is subdivided into annuli by much shallower ones. This is 
evident both on the dorsal and ventral surface, but more so on the ventral, where the 
furrows have been made still deeper in consequence of the curvature of the body. In 
fact, when the animal is seen from this side, the furrows marking the boundaries of 
somites appear so conspicuous that all others look like mere wrinklings (pi. vii, fig. 5). 
The skin is on the whole smooth, there being neither papillae nor tubercles to 
roughen the surface. The segmental sensillae, so constant and regularly arranged in 
many Hirudinids, could not be detected externally, though such organs were observed 
here and there in sections. 
The colour of the specimens preserved in alcohol is a uniform ash-grey without 
any trace of pattern or streaks. One individual which was somewhat darker than 
the others was found under a dissecting lens to be mottled all over with minute dots 
of a darker tint. 
The details of annulation of one of Dr. Annandale's specimens are exhibited in 
pi. vii, figs. I and 2. As stated above, no difficulty is experienced in determining the 
boundaries of somites, which are very distinct externally. Even near the anterior 
and posterior extremities, where the somites are shorter and have less number of 
annuli than in the middle region, the limits are quite obvious. The counting of the 
annuli is, on the other hand, not so easy, as some of the furrows separating them are 
found on the dorsal side or at the lateral margins only, so that we have different 
number of annuli according to" how and where we count thein. 
Counted on the dorsal side there are about 108 annuli in front of the posterior 
sucker. They are grouped into twenty-seven somites as follows: — 
Somites. No. of annuli. 
I, II, III . . . . . . - I 
IV, V . . . . . . . . . . 2 
VI, VII .. .. .. .. ..3 
VIII, IX . . . . - 4 
X— XXI .. .. .. -5 
XXII, XXIII .. .. .. -.4 
XXIV, XXV . . , . . . . . . . 3 
XXVI . . . . . . . . . . 2 
XXVII .. .. .. -.1 
On the ventral side some of the typical five-ringed somites appear to have one ring 
less, the first annulus, which is very narrow, being hidden in the deep furrow imme- 
diately in front of it. Thus, in fig. 3 somites XI and XII are represented as consist- 
ing of four rings only. Where two consecutive somites have the same reduced num- 
