500 A. E. Verrill — Marine Planar ians of JVeic England. 



sucker well-developed, variable in form according to the state of 

 contraction. It is able to swim rapidly with undulatory motions like 

 those of a leech. 



Ocelli two, black, conspicuous, near together, not far from the 

 front end. Pharynx conspicuous in life, as a white median, cylin- 

 drical, sulcated organ showing through the integument ; its open 

 end is divided into about six small lobes. Mouth neai*ly central, 

 or a little behind the middle. Transverse branches of the intestine 

 numerous and crowded, about twenty-five to thirty principal ones 

 on each side; mostly forked and lobulated distally, in adult speci- 

 mens. The ovaries or germaria appear as somewhat opaque, whitish, 

 round or pyriform organs near the bases of the fourth pair of 

 branches of the stomach, and often about midway between the brain 

 and the base of the pharynx. 



Color whitish, grayish, or yellowish ; the intestinal branches 

 usually forming a central darker brown region, in the middle of 

 Avhich the pharynx forms an oblong white spot. The color of the 

 gastric or intestinal branches varies according to their contents. 



Length 15 to 25"""; breadth 4 to 6"'"\ 



Cape Hatteras, N. C, to Casco Bay, Maine, Very common on 

 the gills and gill-plates and other parts of the " horse-shoe crab," 

 Limulus polyphem us. 



The egg-capsules* are often found in large numbers attached to 

 the gill-plates of Limnlus. They are chitinous, brownish or yellow- 

 ish, variable in size and form, usually oval, elliptical, or oblong, 

 with the upper side convex and the under side nearly flat ; the 

 larger ones are about ^^^ long and half as wide. PL xLiv, figure 

 Sh. They are usually attached by a pedicle at one end, but some- 

 times at both ends. They contain from one to eight eggs or em- 

 bryos, most commonly four to six. I have observed fresh capsules 

 during the whole summer, and have seen them forming in October, 

 showing that the breeding season is long. PI. xliii, fig. 11, ca. 



It seems to me certain that the embryos formerly described and 



* Dr. J. A. Ryder has described and figured three forms of these egg-capsules from 

 the gills of Limulus (Amer. Naturalist, vol. 16, pp. 48-51) and thinks that they prob- 

 ably belong to distinct species. I have never found but one species of adult plana- 

 rians on Limulus. In the case of one of the worms (fig. 8), supposed by him to be 

 a distinct species, he mistook the caudal sucker for the head, and overlooked the eyes. 

 Making this correction, the differences noted by him disappear. The differences in the 

 capsules appear to be only variations of form and size of no great importance due, in 

 part at least, to the age and size of the individuals producing them. The capsules 

 produced by the largest specimens contain more ova than those belonging to young 

 individuals. 



