CASTLE: NORTH AMERICAN RHYNCHOBDELLID^. 47 



In addition to the spots which fall into rows as just described, a few spots 

 are usually found scattered more or less irregularly over the surface of the 

 body. 



Two interrupted brown lines (Figure 30) appear in a paramedian position 

 on the dorsal surface, the interruptions being due to the segmentally arranged 

 white spots of the paramedian rows. A pair of similar, though fainter, dark 

 lines is found on the ventral surface ; but they are farther apart, including 

 between them about the middle third of the ventral surface. The dorsal para- 

 median lines include between them (in the middle of the body) about one 

 fourth of the width of the dorsal surface, which part is usually rather more 

 heavily pigmented than the more lateral portions. 



A median, clear, unpigmented band extends the entire length of the body 

 on the ventral surface. The median row of light spots on the dorsal surface 

 often run together in the posterior third of the body, forming a continuous light 

 vitta. 



Examining more minutely into the coloration of the animal, one finds that 

 it is due to the same two classes of cells as produce the coloration of most other 

 species : first, pigment cells proper, — " excretophores," Graf ; and secondly, 

 reserve-food cells. 



The pigment cells proper, as in other species, occupy a superficial position 

 in, or immediately underneath, the epidermis. They are stellate or richly 

 branched, and are more abundant on the dorsal than on the ventral surface ; in 

 small individuals they are almost entirely wanting. The pigment in immature 

 animals is a rust-colored or dull reddish-brown, but in full-sized animals it is 

 usually dark-brown. 



There is no pigment anterior and lateral to the eyes, nor in the white 

 spots already mentioned. The pigment is more abundant than elsewhere 

 in the paramedian dark lines, indeed its abundance there produces those 

 lines. 



The reserve-food cells in this species, as in G. fusca, are of two forms : first, 

 the ordinary form of large reserve-food cell distributed irregularly through the 

 deeper parts of the body ; secondly, a special form of reserve-food cell, smaller, 

 and more superficial in po.sition, and found only in the white spots already 

 described. 



The ordinary reserve-food cells are large and rounded in outline, often at- 

 taining a diameter of forty mikra or more. They contain rounded granules of 

 a bright green color both by reflected and by transmitted light. It is this 

 form of cell which gives to the small, immature individuals their green color, 

 and often imparts a greenish tone to the brown-colored adults. 



The special form of reserve-food cell agrees closely both in appearance and in 

 distribution with the similarly designated structures of G. fusca. It is found, 

 as already stated, only in the white spots of the dorsal surface ; cells of this kind 

 occur in a group of from two to a dozen or more each, situated in the centre 

 of a white spot, just underneath the epidermis. By reflected light they are of 

 a light lemon-yellow color ; by transmitted light, greenish -brown. 



VOL. XXXVI. — NO. 2. 3 



