277! TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 83 



depends upon the functioning of the other. There are four types of locomotion : 

 first, free swimming movement where there is no twisting or turning of the body; 

 second, free swimming where the whole body rolls spirally; third, a creeping 

 or crawling over surfaces in which instances the movement may be entirely 

 a gliding or slipping, or may be by muscular contraction; fourth, a scrambling 

 or wriggling thru masses of silt or debris. In the first type of movement, the 

 cilia are large and evenly distributed over the whole body and the muscular 

 system is used only for special contraction. Strongylostoma rosaceum is an 

 example of this sort. The second method, of rolling over and over, is illus- 

 trated by the habit of Stenostoma, where the spiral twisting is very marked. 

 Again in such forms as habitually creep or crawl, the cilia are generally ex- 

 tremely fine while the muscular contraction of the body as a whole is well 

 developed and is constantly used. Examples of this sort are furnished by 

 Macrostoma album and the several genera of the Prorhynchidae which always 

 cling to some surface and do not let go, so that they never swim out unprotected 

 into the water. The different species of Mesostoma also have this same habit. 

 These forms may be said to be lurking animals or bottom inhabitants, never 

 found in open water. Upon occasion when hunting in a mass of algae, any 

 form may make use of both muscular system and surface cilia in climbing 

 around and thru tangled filaments, but generally where the activity is muscular 

 the cilia are very small. This correlation of cilia size with muscular, develop- 

 ment is a notable one in all the rhabdocoel families. 



Other characters of comparative importance are the relative thickness of 

 integument, heavy eye pigment, and extremely specialized pharyngeal appara- 

 tus. The outline on the following page summarizes the most conspicuous 

 points in this study. 



