160 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



XVII. THE GENERAL ANATOMY OF THE LEECH. 



Macrobdilla decora. 



I. SPECIMENS for examination should be killed with chlo- 

 roform, and they may then be examined, or they may be 

 preserved in alcohol. If the large pond leech cannot be 

 procured, the medicinal leech may be used. Examining 

 a fresh or an alcoholic specimen, notice the following ex- 

 ternal characteristics. 



a. The arched, dorsal surface of the long, ribbon-like 

 body. This surface is distinguished by its dark, olive- 

 green color, as well as by the regular arrangement of the 

 pigment spots. 



b. The flattened, light-colored ventral surface, upon 

 which the pigment spots are very irregularly distributed. 



c. The anterior end of the body may be recognized by 

 its protrusible proboscis, or sucker, which is formed by 

 the upper lip, and projects over the mouth. 



d. The posterior end of the body terminates in a much 

 larger sucker, with an unbroken circular outline. The 

 disk of the posterior sucker is imperforated, and faces 

 ventrally. 



e. On the dorsal surface, note : 



1. The annuli or rings which encircle the body. These 

 are about one hundred in number, and must not be mis- 

 taken for the true somites into which the body is divided. 



2. The proboscis is made up of four incomplete annuli, 

 and the first complete ring. 



3. The ten black eyes, which are arranged in a horse- 

 shoe upon the dorsal surface of the anterior end of the 

 body. 



