64 ANIMAL FORMS 
outer surface is delicately marked off into eighty or a hun- 
dred rings, of which from three to five are included in one 
of the deeper true segments corresponding to those of 
other annelids. From two to ten pairs of simple eyes are 
borne on the head, and owing to the fact that they are 
active swimmers, or move by caterpillar-like looping, loco- 
motor spines are unnecessary and absent. In their internal 
organization, however, there are many features which in- 
dicate a close relationship with the Oligochetes or few- 
bristle worms. The nervous, circulatory, and certain char- 
acteristics of the excretory systems are decidedly similar, 
but, on the other hand, some facts are difficult to explain 
on such a theory, and have led some zoologists to the belief 
that the relationship of these animals can not at present 
be determined. 
67. Haunts and habits —The leeches usually dwell in 
among the plants in slowly running streams, but some 
occur in moist haunts on land, and a considerable number 
live in the sea. All are “bloodsuckers ”—fierce carnivo- 
rous worms, whose bite is so insidiously made that the vic- 
tim frequently is ignorant of their presence. Fishes, frogs, 
and turtles are the most frequently attacked, but cattle and 
other animals which come down to drink also become their 
prey. In some of the tropical countries the land-leeches 
are present in large numbers secreted among the leaves, and 
so severe are their attacks that various animals, even man, 
succumb to their united efforts. Adhering by their suck- 
ers, they puncture the skin, some using triple jaws, and 
fill themselves until they become greatly distended, when 
they usually drop off and digest the meal at leisure. In 
certain species the intestine is provided with lateral 
pouches (Fig. 40), which serve to store up the food until 
the time for digestion arrives. A full meal is sufficient 
with some species to last for two or three months, and the 
medicinal or horse-leech when gorged with food may con- 
sume a year in digesting it. 
