THE WORMS 81 



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 Oligochsetes or few- 

 bristle worms. The nervous, circulatory, and certain char- 

 acteristics of the excretory systems are decidedly similar, 

 but, on the other hand, there are some facts difficult to 

 explain, which have led some zoologists to believe that 

 the relationship of these animals can not at present be 

 determined. 



77. 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. 45), 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. 



