CASTLE: NORTH AMERICAN RHYNCHOBDELLIDA). AT 
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 position, 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 
