84 ILLINOIS BIOLOGICAL MONOGRAPHS [in 



SUMMARY 



1. In swiftly flowing streams where a rocky bed furnishes a sheltered place 

 of attachment, planarians and a few creeping rhabdocoels find a suitable 

 location. 



2. For most of the free-swimming species, ponds and temporary puddles 

 supply the best conditions. Such a situation comprises: first, a protected 

 retreat and also a feeding ground which may be found in a mass of filamentous 

 algae; second, a source of food which may be found among the animal com- 

 munities. 



3. The response to the presence or absence of oxygen and carbon dioxide 

 is more precise than that caused by any other stimulus. 



4. The reaction to light varies in different species but in most instances is 

 negative tho not definitely so. 



5. Response to temperature is general or diffuse, rather than to a localized 

 stimulus, as, for example, the seasonal change in the condition of the water. 



6. Since nourishment is gained mostly from disintegrating protoplasm, 

 the food relationships are very simple and altho nearly defenseless the Tur- 

 bellaria seem to have few enemies. 



7. The new species, Stenostoma giganteum, Stenostoma glandiferum, Mac- 

 rostoma album, Dalyellia alba, Dalyellia niegacephala, Strongylostoma rosaceum, 

 Mesostoma angulare, Mesosioma simplex, are described carefully both as to 

 structure and also as to the precise conditions of existence under which they 

 may be expected to occur. 



