CASTLE: NORTH AMERICAN RHYNCHOBDELLID&. 35 
rounded clear spots of approximately the same form and position as the yellow 
pigment spots found on the posterior sucker of G. parasitica (see stippling in 
Figure 6). 
4, The sensory ring of each of the somites in the neck region — somite vy. 
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 body. 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 difference 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 body, in about the position of those found both dorsally 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, we 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. 
