20 ILUNOIS BIOLOGICAL MONOGRAPHS [214 



develop slowly or lie dormant for some time, if deposited in the fall, will be 

 ready to begin a more rapid growth in the spring. 



In the matter of food, the turbellarian is not fastidious. Many pieces of 

 animal and plant material find their way bit by bit into the tiny and apparently 

 IneflBicient mouth of the hunters. Plant food seems to be second in choice, 

 probably because the thick cellulose of its epidermis is too armor-Hke and is 

 beyond the possibihty of even receiving an impression from the deUcate and 

 jawless lips of these gentle feeders. Even the finest of the filamentous algae 

 are themselves as large as many of the rhabdocoels and too stiff to be managed, 

 while the lower forms, such as the flageUate swarm-spores and the like, are as 

 a general rule too swift and active to be caught aHve. Even the planarians seem 

 to prefer a more easily assimilated food. When, however, algal cell walls are 

 broken down, so that the inclosed cytoplasmic content becomes available, 

 either free in the water or adhering to its original position, then it is greedily 

 sucked up by almost any species. As soon as any of the lower plant forms 

 begin to disintegrate, then they become a probable food supply. 



The obtaining of animal food is also difficult, since only the soft parts can 

 be used. The entomostracans, rotifers, and similar types, furnish large 

 amoimts of food as soon as the individual dies, but they are seldom attacked 

 when alive. In one instance, only, has a rhabdocoel been seen making an 

 attempt on the Ufe of a rotifer. For five minutes they struggled, but the roti- 

 fer held its ground and the rhabdocoel finally left. The chitinous shield of 

 small crustaceans armed with spines or other projections is formidable, but 

 as soon as the segments of the body thru disintegration begin to fall apart, 

 then it is possible for the rhabdocoel to crawl inside and, thus protected, clean 

 out the soft parts at its leisure. Protozoa probably make ideal food because 

 their protoplasm is generally not so thoroly covered as to be inaccessible 

 and because they are common everywhere. In those species where a cal- 

 careous shell is secreted, the rhabdocoel swallows the whole, digests out the 

 protoplasm, and then ejects the hard parts. Tho the planaria are often de- 

 pendent for their food on disintegrated fine organic debris, yet when the 

 opportunity offers they make the most vigorous efforts to obtain the flesh 

 of higher animal forms. 



As a whole, the turbellaria are scavengers, Hving upon bits of disinte- 

 grating organic matter. In the general life constituency of a pond commimity, 

 they play an important part, constantly searching out and devouring particles 

 which might later be a source of bacterial growth. The smaller rhabdocoels 

 can be found in great numbers, incessantly hunting thru the mazes of algae 

 for dead crustaceans, etc., or burrovang and worming their way thru the loose 

 earth-Uke masses on the surface of the bottom. Here they find what is left 

 of myriads of protozoa and also other material, either plant or animal, which 

 they speedily devour. 



Animals with feeding habits such as these would seem always to have more 

 than a sufl&ciency of food supply at hand. This is not always the case, how- 

 ever. Under special conditions, other worms or larger species may keep the 



