WOODWORTH: ILLINOIS TURBELLARIA. 5 
may be as few as two, nor is the number always the same on both sides. I 
have never observed more than a total of eight eye-spots in D. lacteum, there 
being from one to six accessory eyes, either equally or unequally distributed on 
the two sides of the head. Girard (1893, p. 165) describes and figures varia- 
tions in the number of the eyes, and also shows the accessory eyes to be smaller 
than the pair of normal eye-spots. Leidy (1885, p. 50) also speaks of the 
accessory eyes. Of the many Illinois specimens of D. lacteum that have come 
under my observation, 33 per cent of the individuals exhibited variations in 
the number of the eyes. 
Anastomoses in the branches of the intestine exist in most of the specimens 
examined ; these are usually confined to the branches of the posterior trunks, 
which are often united by transverse commissures. In one case there were three 
such transverse commissures. Girard (1893, Pl. 4) figures an individual in 
which the posterior trunks can no longer be recognized as such, the digestive 
tract existing as a meshwork or reticulum. Leidy (1885, p. 50) and Iijima 
(1884, p. 390) also mention anastomoses, and the latter figures a commissure 
uniting the posterior trunks, while Wheeler (1894, p. 176), in a species 
which he believed to be D. lactewm, failed to detect any such connections. 
Hallez (1892) also figures such connections for this species. 
I have little to add to the account of the sexual organs given by Tijima, 
but do not find the penis to be so nearly spherical in shape as that figured by 
him. The shape of the male organ is more like that figured for D. lacteum 
by Schmidt (1861, Taf. 1V.), longer and more cylindrical. Nor is the cavity of 
the penis so large as that figured by Tijima, the muscular walls being much 
thicker (Figs. 10-12). The cavity of the penis is lined with a glandular epi- 
thelium, which projects into the lumen of the organ in folds, thus producing a 
large secreting surface. It is possible, of course, that the cavity varies at 
different periods of sexual activity. In one important particular only do my 
observations on the sexual organs differ from those of Iijima. According to 
that author the vasa deferentia open separately and directly into the cavity of 
the penis and at considerable distance from e 
h other. My observations do 
not confirm the existence of such conditions, but show that the vasa defer- 
entia unite into a slender ductus ejaculatorius, which extends in the longi- 
tudinal muscles of the organ along its ventral surface to that point where 
the penis begins to taper off to form the slender distal free intromittent part of 
the organ (Fig. 10). At this point, which may be designated as the root of 
the penis proper, and corresponds with the posterior limit of the glandular 
cavity, the duct becomes confluent with the cavity of the penis. In other 
words, the glandular cavity of the penis may be said to pour its secretions at 
this point into the seminal duet, and the greater mass of the penis can be com- 
pared to a prostate gland, the Kórnerdriise of Polyclads. In transverse sec- 
tion it is often difficult to follow the course of the duct, owing to its small size 
and to the fact that the lumen is often obliterated by the approximation of its 
walls, and frequently lies in one of the glandular folds projecting into the cavity 
of the organ (Fig. 12). The sheath of the penis in its deeper portions is thrown 
