CASTLE : NORTH AMERICAN RHYNCHOBDELLID^. 35 



rounded clear spots of approximately the same form and position as the yellow 

 pigment spots found on tiie posterior sucker of G. parasitica (see stippling in 

 Figure 6). 



4. The sensory ring of each of the somites in the neck region — somite v. 

 and a few of the following — is occasionally distinguished by an uninterrupted, 

 but narrow, clear band, which runs entirely across it from one side of the body 

 to the other, occupying about its middle third. 



The conspicuousness of the unpigmented areas just described, except that 

 mentioned under (4), is increased by the presence in the centre of each of 

 a group of peculiar reserve-food cells, which lie quite near the surface of 

 the body. 



The ordinary reserve-food cells of this species agree in practically every par- 

 ticular of structure and distribution with those of G. stagnalis. They are large 

 rounded cells, sometimes attaining a diameter of eighty mikra or more. The 

 granules within their cytoplasm attain a diameter of six or seven mikra. The 

 color of these cells by reflected light is a pale orange ; by transmitted light, 

 they are semi-transparent, of a leaden gray color. They are distributed ir- 

 regularly through the middle and posterior portions of the body, being situated 

 in its deeper parts. 



The special form of reserve-food cell, which is found in the segmental clear 

 spots already described, differs in respect both to size and to color from the ordi- 

 nary reserve-food cell. It is considerably smaller, — forty to fifty mikra being 

 the maximum diameter observed, — and its contained granules are likewise 

 smaller, though more numerous. Its color by reflected light is a bright lemon 

 yellow ; by transmitted light it is brown. Finally this variety of reserve-food 

 cell is invariably situated quite near the surface of the bod)'. The appearance 

 of a group of these cells as seen under a moderately high power of the micro- 

 scope is shown imperfectly in Figure 17 (Plate 4). 



The ventral surface of the body is pigmented in very much the same fashion 

 as the dorsal, but less heavily. There is, however, this difi'erence in the dis- 

 tribution of the superficial brown pigment : on the ventral surface a pair of 

 narrow, paramedian, pigmented lines can be recognized, one in each half of 

 the bodj'', in about the position of those found both dorsjdly and ventrally in 

 G. elegans (Figure 30, Plate 7). On the dorsal surface, on the other hand, 

 the most heavily pigmented region is a broad median band (p. 34). 



Segmental clear spots are found on the sensory rings on the ventral surface 

 also, and these are arranged in paramedian, intermediate, or marginal rows', 

 but the spots are much less conspicuous than on the dorsal surface, and the 

 lemon-yellow reserve-food cells are less often found in their centres. 



Comparing the coloration of this species with that of G. stagnalis, Ave may 

 say that the histological elements which produce the coloration are very similar 

 in the two, but the distribution of these elements is such as to produce in G. 

 fusca a distinct color pattern (longitudinal striations and segmental clear spots), 

 a feature entirely wanting in G. stagnalis. 



