ioo THE LEECHES OF MINNESOTA 



in the fashion of a glossiphonid. Four somites of simple structure 

 enter into its composition, the posterior ventral rim heing formed by 

 the fourth and fifth somites in that region largely coalesced. On the 

 middle of somite III is situated the single pair of small eyes conjoined 

 in a single median pigment mass and looking forward and outward. 

 Some detached pigment cells occur caudad and lateral of this position. 



Most remarkable of all of the external features of this leech is 

 the posterior sucker. It is much wider than any part of the body, 

 largely free around its entire circumference and supported by a narrow 

 central pedicle. The ventral surface is very deeply cupped and the 

 rim somewhat contracted, making the diameter of the opening some- 

 what less than that of the internal cavity. From the internal face of 

 the sucker, a short distance back from the sharp margin, spring about 

 thirty (thirty in one, twenty-nine in the other, specimen) slender 

 finger-like papillae which project more or less freely beyond the 

 margin. Owing to their contractile nature they vary in length and 

 diameter but when extended the longest are about .4 to .5 mm. in 

 length and about .1 mm. in diameter. Each one contains an axial 

 gland duct or group of ducts surrounded by a sheath of muscle fibres 

 which spring from the muscular ridges passing radially down the 

 inner face of the sucker. The gland ducts arise from a circle of glands 

 which appear as a circle of whitish spots arranged around the sucker 

 about midway between the margin and the pedicle and which raise the 

 outer surface into a slightly marked encircling ridge. 



A median series of rather prominent conical papilla; with the 

 long diameter of their elliptical bases directed in the longitudinal axis 

 of the leech occur on the large annuli b^ and b$. In the Lake Pepin 

 specimen these papillae begin on VIII &5 and continue to XXVI &j; 

 in the type they are distinctly developed only on the somites XI to 

 XXV inclusive. In the new example also traces of supra-marginal 

 and intermediate series of papillae are found on the somites of the 

 middle region. Segmental sensillae are very beautiful and regularly 

 shown in this specimen on all of the somites and both dorsally and 

 ventrally. The position of those found in the type and shown in the 

 figure of that specimen is confirmed and in addition the presence 

 of supra-marginals and of six ventral series is established. Thus it 

 will be seen that the sensillae have the arrangement characteristic of 

 the Glossiphonidcc. Well developed rings pf small sense organs are 

 visible on annuli b2, b^ and &5 of each of the complete somites and 

 are more or less discernible on all primary annuli and more compre- 

 hensive divisions throughout the body. 



