44 ILUNOIS BIOLOGICAL MONOGRAPHS [238 



depth is exceedingly slight. The head is sharply truncate, square with the 

 ciliated pits smaller than is reported for other forms. The posterior half of 

 the body is much larger and darker than the European type, showing a greatei 

 contrast with the margin and with the head which is extremely transparent. 

 The pear-shaped cells in the integument seem to be more conspicuous than is 

 usual, as they are clearly outlined against the rest of the epithelium. Since 

 there are very many, they are arranged close together. The parts of the struc- 

 ture appear clearly. A large outside portion made of a single cell with thick 

 definite wall contains an eccentrically placed smaller part round and dark 

 in color. This evidently bears some relation to the nematocysts and rhabdites 

 of other species. These details are of some interest in showing the amount 

 of variation in a single form. 



Prorhynchus applanatus Kennel 1888 



During the month of February, in collections from under the ice, individuals 

 of this species appeared crawling in masses of Cladophora. This is a very 

 different habitat with different environment from that of a greenhouse where 

 it has been foimd before. The animal was noticeable on accoimt of its pure 

 white color and quick jerky movements as it crawled thru heavy tangles of 

 alga or hurried over the side of the aquarivun jar. In a few respects it differs 

 from the type descriptions. The body is not more than 3mm. long when fuUy 

 extended and about one-fifth as broad. It is extremely flat on the dorsal side, 

 the arching over the intestine being slight. The shape as a whole is not so 

 slender as in Kennel's drawings, being nearly an oblong with parallel sides and 

 nearly parallel ends. The anterior surface is deeply notched at the point of 

 the mouth opening, giving the two lateral corners an almost lobe-like appear- 

 ance. This, with the clear transparency, makes the head-region conspicuous. 

 The tail end is much more rounded and short than in other cases, which causes 

 the whole body to seem broader. The color as a whole is a much denser and 

 purer white than that of Prorhynchus stagnalis, showing a yellow tinge only over 

 the intestine. 



The pharynx shows clearly its division into heavy, large secondary cells 

 which act as a support for the four pointed tooth-like cells which work in 

 connection with each other and recall the Aristotle's lantern in the Echmoid. 

 They are relatively large and muscular, occupying one-fiftli the body length. 

 The method of working is peculiar, as the movement is entirely confined to the 

 narrow space within the pharyngeal wall. There is little expansion and the 

 limits of motion are narrow. This is balanced by the drawing backward and 

 forward of the whole structure which gives a purchase on whatever material 

 is held at the mouth opening. The intestinal diverticula are large but very 

 irregular and many are not straight but curved and bent. This differs from 

 the extremely even condition in the original type. 



One other detail might, perhaps, be mentioned, the small size of the eyes. 

 They were of the same bright color but were not more than one-half the size 

 given for the European specimens. 



