168 
The British Leeches 
conspicuous feature consists of a pale median, longitudinal band, mar¬ 
gined with black, alternately wdde for the length of three rings and 
narrow for the length of two rings. The constricted portions of this 
band correspond to rings 3 and 4 of each somite and the dilated 
portions traverse rings 5, 1 and 2 of contiguous somites. Adults are 
blackish green, olive green, yellowish green or brownish, paler and often 
bright green ventrally, and more or less densely flecked with black above 
and below. The geometrical pattern seen in young individuals is almost 
or entirely obliterated. The pale, median dorsal band sometimes may 
be braced in favourable examples of light colouration ; its black margins 
frequently persist in the form of two somewhat broken and irregular 
black stripes. 
102 rings. Rings 6 and 7 are united ventrally to form the posterior 
margin of the anterior sucker. Rings 8 and 9 are also fused on the 
ventral side. The last ring (102), which is pierced by the large anus, 
may show signs of sub-division : Whitman (1886, pp. 371—372) assigns 
to it the value of two rings. 
Somites I, II, III and XXVII, uniannulate ; IV, XXV and XXVI 
biannulate; V, VI, VII and XXIV triannulate; the sixteen somites 
VIII—XXIII are complete with five rings. 
The five pairs of eyes lie respectively in rings 2, 3, 4, 6 and 9. 
[Note. The disposition of the eyes and the external metamerism, except 
in the case of somite XXVII, are the same as in Hirudo medicinalis. 
In the latter leech somite XXVII is biannulate and consequently its 
body possesses one ring more than Haemopis sanguisuga .] 
Oesophagus with twelve longitudinal plications, the three largest 
ending anteriorly in jaws. 
Each jaw is armed with 11—18 pairs of irregular, blunt teeth 
(R. Blanchard). 
The male genital orifice is situated between rings 31 and 32, that is 
between the second and third ring of somite XI, or upon ring 32 ; the 
female orifice lies between rings 36 and 37, that is between the second 
and third rings of somite XII, or upon ring 37. One or both of these 
orifices may thus be shifted forwards by the space of half a ring ; 
normally they are separated by the space of five rings. 
Size. The following dimensions apply to average, medium-sized 
individuals: 
In contraction, 25—35 mm. long and 10—12 mm. wide. Fully 
extended 90—100 mm. long and 5—6 mm. wide. Individuals occur, 
