WOODWOKTH : ILLIXOIS TURBELLAEIA, 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, eitlier 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, PI. 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 lijima 

 (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. lacteum, 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 lijima, 

 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. IV.), longer and more cylindrical. Xoristhe cavity of 

 the penis so large as that figured by lijima, 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 lijima. According to 

 that author the vasa deferentia open separately and directly into the cavity of 

 the penis and at considerable distance from each other. My observations do 

 not confirm the existence of such conditions, but show that the vasa defer- 

 eutia 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 oS to form the slender distal free intromittent part of 

 the organ (Fig. 10). At this point, which maybe 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 duct, and the greater mass of the penis can be com- 

 pared to a prostate gland, the Kornerdriise 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 



