218 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
posterior half (representing 62) of the first annulus, while the paired spots are confined to the anterior 
half (61) of this annulus. The black pigment of the intermediate band is entirely, and that of the 
lateral hand nearly, absent from the fifth (6 6) annulus, while the anterior portion of the first or 
double annulus ( 61 and 62 ) is also free from black pigment. On the triannulate somites vii and vi 
this arrangement is still more striking, and the exact composition of the first and third annuli is 
indicated by the extent of the metameric and intermetameric pigmentation. The median black dash, 
the intermediate ellipses, and the lateral crescents on each occupy the middle annulus and about the 
adjacent one-half of the third (a3) and two-thirds of the first (al) annuli, while the paired inter- 
metameric spots are confined to exactly the remaining fractions of annuli «1 and a 3. These parts 
have exactly the values which were assigned on other grounds to 61 and 66 in the composite annuli. 
Even on the biannulate somite v the pattern remains; the median dash becomes a mere spot, which 
occupies about the posterior three-fourths of the first (al and a2) and the anterior half of the second 
(«3) annulus. Anterior to this the median line becomes continuous over somites iv and in to a point 
between the first pair of eyes, where it meets the light color of the lip margin. The remains of the 
intermediate and lateral bands, and especially the intermetameric spots of the median band, serve to 
define the potential annuli even on somite iv, the last named extending onto the posterior part of hi. 
It will be seen that the study of the color pattern of this species confirms to the last detail the values 
which were assigned to the annuli as a result of the study of sense organs, integumental furrows, etc. 
Further, it affords support to the neuromeric standard for limiting the somite. 
At the posterior end of the body a similar relation between the color markings and the somite 
constituents appears to be maintained, but the condition of the material prevents its being satisfactorily 
worked out. The posterior sucker is marked above by an irregular ring of black inclosing a light 
spot and flanked by a few black rays; the ventral surface is ash-colored, with a few small scattered 
black spots, mostly near the margin. 
Small specimens are still brighter in color. The ground is purer and clearer, sometimes paler, 
sometimes redder, and the black markings relatively deeper and more vivid. As the size increases 
there appears to be a progressive tendency for the black pigment to diffuse over the entire dorsal 
surface, changing the ground color to a dull olive and entirely obscuring the markings, though the 
more important black spots may always be found. The largest specimen is of a nearly uniform brown 
olive, with faint darker cloudings, spots, and broken lines, among which may always be distinguished 
the median series of dashes, the paired intermetameric spots, and the lateral spots. They are very 
obscure, but sufficient to show the persistent impress of the original pattern. 
Alimentary Canal . — The mouth cavity is hounded posteriorly by three broad triangular folds, a 
single median ventral and a pair of dorso-lateral, together forming a diaphragm, through the limbs of 
the trifid aperture of which the anterior edges of the three jaws are usually visible. Slight grooves 
run along the bases of the dorsal folds and meet in a triangular expansion of the median labial t ' us. 
Except that the median dorsal jaw is somewhat lower, the three jaws (pi. 12, fig. 5) are of simiiai 
shape — long, low, and compressed, with the edge only slightly convex. They are strongly angulated 
anteriorly, where they pass abruptly into the supporting plate, but recede more gently behind. The 
denticles (pi. 12, figs. 5 and 6) are very small, triangular plates set transversely on the jaws, and 
number from 160 to 180 on each jaw in the two examples which were examined. They are largest 
anteriorly, where they measure 0.03 mm. in height, and diminish gradually to one-half that height 
at the posterior end. Along the sloping sides of each jaw are considerable numbers of button-shaped 
papillfe supported on narrow stalks. They vary in size, the largest being about 0.07 mm. in diameter, 
the smallest about one-fourth that size. Most of them are arranged somewhat in three irregular rows 
(fig. 5) of about ten each, between which some smaller ones are scattered. They appear not to be 
sense organs, but serve as places of exit for some of the ducts of the pharyngeal glands, most of which 
traverse the interior of the jaw and open on its ridge between the teeth. Possibly it is due to the 
great number and crowding of the denticles that additional outlets are required for the glands. 
The muscular oesophagus is marked by six longitudinal folds, the three which correspond to the 
jaws being larger than those which alternate with them. It reaches to somite ix. There are ten 
pairs of gastric caeca developed, as in Ilirudo. The last originates in xix, is large, sacculated, and 
extends caudad. None of the smaller caeca are much sacculated. That this species is a true blood- 
sucker is shown by the presence of blood in the caeca of all specimens examined. 
Reproductive Organs .- — A general view of the reproductive organs is shown in pi. 12, fig. 7. The 
male organs do not differ in any important respect from Hirudo, though the sperm sacs me) are larger. 
