28 ILLINOIS BIOLOGICAL MONOGRAPHS [222 



The food relationships are more complex than appears at first. How many- 

 enemies there may be is hard to ascertain. That Stenostoma becomes the 

 food of other species is not easily determined since the body is entirely of 

 soft parts and quickly disintegrated. They seem not to be hunted down by 

 other forms to any great extent, except in the case of some few fishes which 

 easily take them along with other microscopic species. When, however, the 

 body structure is disintegrating, the protoplasmic content within the rhabdite- 

 bearing integument is good food for almost any form. They can hardly be said 

 to form any conspicuous part of the food of an animal. The food they eat is 

 of much more interest and importance. To some extent they are scavengers, 

 eating the disintegrating organic material so plentiful in the surface of the 

 bottom-mud, or entangled in masses of filamentous algae. They are voracious 

 hunters and can nearly always be found working their way, truly worm-like, 

 thru the soft silt, systematically seeking out every bit of available nutrient 

 material. They also evidently swallow much indigestible matter, as 

 after a period of feeding in such a situation, the intestine will be found 

 almost black and later this residue will be seen extruded thru the mouth, 

 sometimes a little at a time, and often in quite large masses. That 

 this common form plays a large part in helping to keep clear the 

 bottom water is very evident. The small algal swarm spores, volvox, 

 euglena, and the lilce, are eaten to some extent, but are probably more or less 

 unpalatable. The food which is the most conspicuous, altho hardly the most 

 com^mon, is made up of the larger animal types, such as ostracoda, glcchidia, 

 encrusted protozoa, and the like. Stenostoma leucops especially seem^s to have 

 a liking for the largest possible morsels, preferring those with a hard shell. 

 Difflugia is, perhaps, the most common form, found lodged in the intestine and 

 is present in even rather small-sized individuals. During a fev/ days, five dif- 

 ferent species of DifSugia have been seen within the digestive cavity of speci- 

 mens from a single pond. The naked protoplasm of the animal part, even 

 tho entirely drawn into its shell, is easily digested out and the comparatively 

 smooth spherical exterior makes a mass easily extruded. The size is also con- 

 venient, not so large but that even the contracted zone of fission may allow it 

 to pass thru to the posterior zooids. In the same way, other small smooth 

 forms seem especially desired. One example will show the tendency in this 

 direction. An individual was noticed swimming around normally except that 

 the movement was a little slow. The shape, however, was conspicuous as 

 the animal seemed to be a tiny cross, very clear-cut and definite. Under the 

 the microscope, the extra structure proved to be a good -sized ostracod lying 

 in the intestinal cavity of the worm at right-angles to the length of the body, 

 and by its bulk causing the body-wall to be pushed out on both sides imtil 

 the protruded part was equal to the other divisions. The animal seemed to 

 sufiFer no serious inconvenience altho the integument and intestinal wall were 

 stretched to the breaking point. Evidences of such inappropriate food are 

 quite common. Any rounded hard-shelled animal seems acceptable either 



