MOVEMENTS, ETC., OF FRESH-W.Vl'ER PLANAKIANS. 535 



tlie animal to the film, the surface tension being' sufficiently 

 great to support a considerably greater weight than that of 

 a flat-worm. 



It is interesting: to note in this connection that the land 

 planariaus are able to move about on the top of the surface 

 film of water to a limited extent (cf. Lehuert, loc. cit., 

 p. 16). The immediate means of support here, as in the case 

 ol the fresh-water planarians, is the mucous secretion. 



The leaving of the surface film by means oE the mucus 

 thread described above apparently does not take place if it is 

 possible for the same result to be accomplished in any other 

 Avay. Before it occurs tlie worm usuall}' stretches the 

 anterior end down into the water, and turns it in all direc- 

 tions. If it comes in contact with something solid the 

 anterior end becomes attached to this, and pulls the posterior 

 end of the body away from the film. If nothing solid is 

 within reach the Avorm will usually, after a time, drop down 

 on a mucus thread as described. 



III. Food. 



Planarians will take almost any sort of animal food very 

 readily. I have used mainly, in the feeding experiments, 

 crushed pieces of fresh- water molluscs, such as I'hysa, 

 Planorbis, etc. One of these molluscs, removed from the 

 shell and placed in a dish containing a large number of 

 planarians, will, in a short time, be literally covered with the 

 worms feeding. If a worm is gently lifted off the pile the 

 greatly stretched phai-ynx will be brought into view. The 

 Avorms will eat any other kind of animal tissue (fresh meat, 

 parts of insects, pieces of fresh-water Avornis, etc.), so far 

 as I have observed, the only condition being that the meat 

 must be fresh. As will be shown later, the juices from the 

 food act as chemical stimuli, so that it is necessary that the 

 tissue be crushed or bruised so that its juices can escape into 

 the water. A partially crushed specimen of Plan aria, even 

 though still able to move about, will be seized upon and eaten 



