IVORMS, CRAYFISH, CENTIPEDS, ETC. 145 



worms of various kinds are found in all parts of the world 

 except in desert or arid regions. In size these different 

 kinds vary from i mm. (g'-j- in.) to 2 meters (2^ yards) 

 in length. 



Leeches (fig. 107) are familiar to boys who go in swim- 

 ming. Some live specimens should be brought into the 

 schoolroom. The body of a leech is flattened instead of 

 being cylindrical as in the earthworm, and tapers at both 



Fig. 107, — A leech, Clepsine, ventral view; posterior sucker at left. 

 (Natural size; after photograph by E. R. Downing, in Davenport's 

 Zoology.) 



ends. In the live animal it can be greatly elongated 

 and narrowed, or much shortened and broadened. It is 

 comiposed of many segments (not as many as there are 

 cross lines, however, each segment being transversely 

 annulated), and bears at each end on the ventral surface 

 a sucker, the posterior one being the larger. These 

 suckers enable the leech to cling firmly to other animals. 

 The mouth is at the front end of the body on the ven- 

 tral surface and is provided with sharp jaws. Leeches 

 live mostly on the blood of other animals. The common 

 leech fastens itself upon its victim by means of its suck- 

 ers, then cuts the skin, fastens its oral sucker over the 

 wound, and pumps away until it has completely gorged 

 itself with blood, distending enormously its elastic body, 

 when it loosens its hold and drops off. Its biting and 



