245] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 51 



In the United States, nine species belonging to this family have been identi- 

 fied. All are from localities in New York except two, Bothromesostoma 

 personatum and Mesostonia ehrenbergii, which have been found in Michigan and 

 Illinois. To this list may be added several others. 



Rhynchoniesostoma rostratum (Miiller) 1774 

 This is, perhaps, the most delicate of all the rhabdocoels. One of the very 

 first to be described, it has appeared again and again in many places. It is 

 naturally a northern form and is found in cold water, under the ice or early 

 in the spring. Von Graff had specimens from a peat bog in Rochester, which 

 measured only 2 mm. Those which I have had come from a small temporary 

 pond having a muddy bottom which was covered with dead leaves, sticks and 

 a little algal growth. The water is never clear and was in the process of drying 

 up. The length is in every instance more than 2 mm. and a few individuals 

 measure 3 mm. All, however, are slender when extended with the anterior 

 and posterior ends drawn out to very long, sharply pointed tips. The whole 

 body makes a very regular spindle with the pharynx protruding only slightly 

 on the rounded ventral side. The proboscis like head is more conspicuous in 

 its contraction than that of the European forms, for it can be drawn back into 

 the body as far as a point even with the pharynx, thus making the anterior 

 end of the greatest width. The two transverse rings of muscle attaclmient 

 are to be clearly seen. A condition opposite to this is found in the tail which 

 is not at all retractile. The color is another noteworthy character. Since 

 the integument is exceedingly transparent, the internal parts are easily dis- 

 tinguishable. The parenchyma in all my specimens is of a clear, pale rose, 

 without the slightest tinge of yellow. Within this the intestine and repro- 

 ductive organs show definite outlines. The wall of the intestine is somewhat 

 gray, with very small ceUs which are nearly all of the same size. Scattered 

 among these are bright carmine red oil globules of about double the size of 

 the other cells and evenly distributed over the outer layer of the digestive 

 tract wall. These help to add to the general reddish color. Of the repro- 

 ductive organs, the ovary, testes, and atrium are grayish with clear, sharp 

 walls, and are not conspicuous. On the other hand, the developing eggs and 

 vitelline glands are of a deep, brilliant red. The glands are compact with irreg- 

 ular lobed margins. They are about one-tenth the total length of the body 

 and lie near the surface on each side at about the middle. They vary in size 

 but not in intensity of color, reaching down to their connection with the atrium 

 as only a very narrow thread. The eggs, either one or two, are matured in 

 the atrium which forms a sort of egg capsule. The color is lodged in the tough, 

 thick shell which is withal sufficiently transparent to show the yolk granules 

 within. These yolk granules when removed from the shell are white and clear, 

 of somewhat varying size. One set of eight eggs measured show^ed diameters 

 varying from 229/i to 288/x. They were very nearly spherical, two diameters 

 in a single egg generally differing not more than 5/i. They lay just behind the 



