26 BRISTOL. [Vol. XV. 



blood vessels, and it is directly over these or some of them 

 that the pigment collects. I hope to make some further obser- 

 vations on this point by raising the progeny of one leech by 

 themselves until they attain the adult markings. 



Description of Ncphelis Lateralis. 



Since the analysis of Clepsine by Whitman (9) has given 

 the prostomium the value of a somite consisting of one ring, I 

 have followed the notation used by him and have counted the 

 prostomium as ring No. i and somite No. i. 



Excepting the clitellum during its active phase, the body 

 is not divided into obvious regions. The oral sucker is not 

 prominent as in some species of Clepsine and the anal sucker 

 is small, exceeding the body but little in width. The male 

 orifice lies normally between rings 36 and 37. The female 

 orifice lies normally between rings 38 and 39 (PL VI, Fig. 3). 



The first pair of nephridiopores lies between rings 16 and 17 

 at the posterior edge of the 7th somite. There are four pairs 

 of nephridia anterior to the male orifice, and these differ from 

 the succeeding nephridia by reduction of certain parts. The 

 pores of the first pair of nephridia behind the male pore lie 

 between rings 36 and 37, about midway between the median 

 plane and the margin, and these are followed in regular order, 

 at intervals of five rings, by the remaining pores. The last 

 pores lie between rings 96 and 97, and the whole number of 

 pairs of nephridia is seventeen. The anus is dorsal and lies 

 behind the 104th ring. 



The clitellum consists of fifteen rings— from 28 to 42 

 inclusive. It includes the last four rings of somite X and the 

 first of somite XIII. It is plainly visible only during sexual 

 activity ; at other times it can scarcely be distinguished from 

 the adjacent rings. In the active condition it is paler in color 

 and may be swollen so as to become larger than any other part 

 of the body. 



^ " The Metamerism of Clepsine." Festschrift fiir Leuchart, p. 395, 1895. 



