No. I.] THE METAMERISM OF NEPHELIS. 29 



The head region consists of the first six somites, comprising 

 the first eleven rings. The first body ganglion lies in the 12th 

 ring, the ist ring of somite VII. 



The 1 8th and last body ganglion lies in the 97th ring, the 

 1st ring of somite XXIV. 



The body region extends from ring 12 to ring 10 1, somites 

 VII to XXIV inclusive. 



The anal region extends from ring 102 to the disc of the 

 sucker; somites XXV, XXVI, and XXVII. 



The sucker contains seven somites, XXVIII to XXXIV. 



Habitat. 



Like other leeches, Nephelis keeps its body for the most 

 part in the dark, and must be sought for according to the con- 

 ditions of the bottom of the pond or stream. In a stony brook 

 or pond beach they may be found adhering to the underside 

 of the stones ; on a sand beach unshaded from the sun they 

 bury themselves almost completely in the sand, projecting 

 their heads at short intervals in search of food. Where the 

 overhanging trees have dropped their leaves into the water 

 they will be found on the underside of the leaves. They may 

 be found on the underside of the water-lily leaves, on floating 

 pieces of wood, and between the bark and the wood of rotting, 

 water-logged branches of trees. 



They thrive under widely different conditions of water, soil, 

 and temperature, so long as food is obtainable. I have collected 

 them in the Charles River at Cambridge, Mass., during low 

 water in midsummer, when the river was reeking with sewage 

 and the chemical wastes from paper mills, while the tempera- 

 ture was but a few degrees lower than that of the air. Yet, 

 within a stone's throw of the river bank I have collected them 

 quite as readily in a clear spring-water brook, in which the 

 water was so cold that collecting in it was almost painful. 

 The abundant food supply appeared to be the only feature 

 common to the two places. 



The character of the bottom of a pond seems to be an 

 indifferent factor, for in the same pond they may be as numer- 



