THE METAMERISM OF NEPHELIS. 



A CONTRIBUTION TO THE MORPHOLOGY OF THE NERVOUS 



SYSTEM, TOGETHER WITH A DESCRIPTION OF 



NEPHELIS LATERALIS. 



CHARLES LAWRENCE BRISTOL. 



NEPHELIS differs from most of the leeches in the absence of 

 well-marked sense organs on the first ring of each metamere, 

 and hence the means usually efficient for determining meta- 

 merism in other leeches is wanting. Professor Whitman had 

 already worked out the distribution of the nerves in Clepsine 

 and found a complete agreement between this and the sensillae 

 (sense organs). It was proposed to apply the same method to 

 Nephelis, therefore, in which form the sensillae were not so 

 apparent. 



A large number of individuals were collected from widely 

 different localities, from Wood's Roll, Mass., to Wolf Lake, 

 near Chicago. Color markings proved useless as criteria for 

 determining species, and the method of counting the rings and 

 noting the variations of size was used. A careful study of all 

 the individuals resulted in placing all the forms in one species, 

 - Nephelis lateralis. This name was chosen because of its 

 priority. The generic name Nephelis was retained also for its 

 priority, though Dr. Blanchard, in France, has brought the 

 name Erpobdella into his descriptions. 



DESCRIPTION. The size of the adult varies from 4 cm. to 

 10 cm. at rest. Anterior to the sexual organs the body tapers 

 slightly to the Vnouth ; posterior to them it continues about 

 the same size until just in front of the anus, whence it 

 tapers to the sucker. A transection of the body is lenticular, 

 though in the clitellar region it approximates a circle. The 

 body flattens in swimming, as in Hirudo and Macrobdella. 

 The color varies from a light chocolate brown free from pig- 

 ment to almost a coal black free from any light areas. The 

 total number of annul! is 106 to the acetabulum. The oral 



