42 ILLINOIS BIOLOGICAL MONOGRAPHS [236 



cells which make up the wall are rather large, and squamous-Hke, but their 

 boundaries are not heavy enough to be clearly distinguishable. They do not 

 show the large oil globules found in many species and the protoplasmic content 

 is much more fluid. 



The nervous system consists of an angular brain ganglion upon whose sur- 

 face the eyes are placed. This is about one-fourth the body length from the 

 anterior end and leaves a broad undifferentiated space before it, a detail which 

 recalls the like condition in Macrostoma sensitivtim. The eyes are dark, very 

 small crescents, placed near together. The diminutive size together with 

 intensity of color, which causes them to be conspicuous against a Hght back- 

 groimd, calls attention to them. There seem to be no other especially devel- 

 oped sense organs, which is not surprising in an animal so sluggish in move- 

 ment and so lacking in definite reactions. 



The reproductive organs are conspicuous because of their opaque grayness 

 and consequent visibility. The testes are distinctly didl colored and extend 

 from the ventral posterior region up around and forward, partially clasping the 

 intestine. The ovaries are just back of the testes on either side. This form 

 differs from others of the genus in that eggs develop in two diverticula of the 

 ovarian ducts. The diverticula are simply expansions of the ovarian wall and its 

 duct and with the enlargement of several consecutive eggs they push forward 

 to a point only a little posterior to the mouth. A nimiber of eggs of various 

 sizes will thus lie in a row on each side of the body, the largest posterior, do^vn 

 near the sexual pore and those farthest forward not more than one-half the 

 size. The female genital pore is very large, situated about one-fifth the dis- 

 tance from the posterior end. It is irregular in shape, and with a thick wall. 

 The male pore is sHghtly posterior and much smaller and thin-walled. The 

 reproductive season is during January and February. Evidences of asexual 

 budding were not present. 



The general points of comparison with other species are briefly: first, dif- 

 ferences in shape; the head is much longer than Macrostotna sensitivum, the 

 tail much narrower than Macrostoma appendiculalum; second, the eyes are very 

 small, much farther back and closer together than in either of the other two 

 forms; third, the male chitinous spicules are shorter, more simple and not so 

 sharply pointed. Other details in which the members of the group show some 

 resemblance are the very light color, the large, hair-hke cilia at the posterior 

 end, the large mouth and comparatively simple intestinal cavity, the position 

 of the ovaries, dorsal to the testes, and the generally spatulate tail. 



A number of specimens of this species have appeared in the ponds near 

 Havana, Illinois, and also at Urbana, showing that the distribution is fairly 

 widespread thruout the state. 



FAMILY PRORHYNCHIDAE 



The family name Prorh\Tichidae was suggested in 1862 by Diesing for the 

 one genus, Prorhynchus, at that time containing a single species, Prorhytichus 



