160 The British Leeches 
of somite III and the third pair is situated in the first ring of somite 
IV. 
The second ring of somite IV, often imperfectly divided from the 
first ring of somite V, forms the posterior boundary of the anterior 
sucker. The mouth opens in somite II. 
Male genital orifice between rings 25 and 26, that is, between the 
second and third rings of somite XI; female orifice two rings behind 
the male, between the first and second rings of somite XII. Testes 
10 pairs. 
Eggs attached to some foreign body and brooded over by the 
parent. 
Anus behind ring 67, separated from the posterior sucker by the 
sixty-eighth and last ring, which is incomplete. 
Length, at rest, 15—20 mm.; width, at rest, 5—9 mm. Length, 
fully extended, up to 35 mm. 
Distribution, Food, Varieties. A sluggish species very readily 
rolling itself up into a ball (like Oniscus) when disturbed; producing 
eggs during April and May, for a period of not much more than four 
weeks and rearing only one brood (Whitman, 1878, p. 10). 
Very common in the British Islands, in running and stagnant 
water, among aquatic plants and upon or beneath stones. It is 
parasitic chiefly upon Limnea and Plcinorbis but also attacks other 
fresh-water molluscs, the larvae of Chironomus (“ bloodworms ”) and 
probably aquatic annelids. Houghton (1865, p. 87) described three 
varieties of this leech and my own observations largely confirm his 
results. English examples resolve themselves more or less into the 
three following forms: 
A. Body greenish, the six dorsal rows of yellow spots well marked 
(the typical form). 
B. Body brown, the brown pigment being disposed in the form of 
minute longitudinal and transverse striae; the six dorsal rows of spots 
more or less dispersed into irregular blotches. 
C. Body olive brown or brown, the pigment not striated, the 
longitudinal dark brown lines less distinct; without spots in regular 
rows ; the anterior pair of eyes sometimes absent. 
I have found A and B about equal in frequency ; C is of rarer 
occurrence and approaches the variety concolor described by Apathy 
from the Danube, and considered by him as a separate species. The 
matter requires further investigation. 
