NATURAL HISTORY OF BRITISH FRESH-WATER LEECHES. 65 
which are repeated at intervals—each repetition corresponding 
~to a somite. The number of rings to a somite is greatest in the 
middle region and decreases towards the extremities, where a 
somite may possess only one ring. 
Distinct patterns are often to be recognised on the dorsal 
surface, and where these are of use in the identification of species 
attention will be called to them. 
A well marked sucker, disc-like in foym, is to be seen at the 
posterior extremity. The mouth functions as an anterior 
sucker, but it is not, as a general rule, disc-shaped. 
The eyes appear as black spots and are placed on the posterior 
surface over the mouth region. They vary in number from 
one pair to five pairs, and their number and position are of great 
value in the determination of species. 
The alimentary canal consists of a straight tube extending 
from the mouth to the anus, the latter being situated on the 
dorsal surface, a little in front of the posterior sucker. The 
alimentary canal is often provided with lobes which serve to 
store the food until digestion is completed. 
In certain species the mouth is provided with three jaws which 
are armed with a large number of teeth. Others again do not 
possess jaws, but have an extensile proboscis. A third series 
have neither jaws nor proboscis. These characters serve to 
divide the class in the following manner. 
Sub-order I. RHYNCHOBDELIYE (Without jaws, but with 
an exsertible proboscis.) 
Family I. Ichthyobdellid^e. (Body cylindrical in fresh¬ 
water species. Anterior sucker discoidal. Eggs enclosed in 
capsules attached to foreign bodies and left by the parent 
to hatch.) 
Family 2. Glossosiphonid^e. (Body ovate, flattened, 
never cylindrical. Anterior sucker not conspicuous. Eggs 
deposited in thin capsules either fixed to a foreign body or to 
the body of the parent, but, until hatched, always brooded by 
the parent, to whose body the young then attach themselves.) 
Sub-order II. ARHYNCHOBDELL^E. (Without a proboscis.) 
Family I. Gnathobdellioe. (With jaws.) 
Family II. Herpobdellid^e. (Without jaws.) 
Space will not permit me to enter into a description of the 
vascular, excretory and nervous systems. These are fully 
