PHYLUM PLATYHELMIA 



175 



that the body may be extended and contracted by muscular 

 movements. A planarian crawls about until it encounters 

 some little animal suitable for food. The proboscis is ex- 

 tended through the mouth (Fig. 73), wraps about the food, 

 and is then drawn into the body. Though a planarian has 

 a pair of simple eyes, they are not used to any extent in 

 seeking or capturing food, but it does have the ability to 

 recognize food through chemical substances given off in 

 the water. If an injured animal is encountered which is 

 bleeding slightly, it will be followed about persistently, but 



FIG. 73. Planarians. The individual at the left id in the act of swallowing 

 a small crustacean. On the right is a planarian which has had its head cut off; 

 the body has regenerated a new head, but the small fragment has formed a two- 

 headed monster. 



a sound and whole individual may not be noticed. Pla- 

 naria's mouth is in a rather strange position, at the center 

 of the ventral surface, but that situation gives good oppor- 

 tunity to stretch the proboscis out in any direction. 



After food has been drawn into the body it passes down 

 the proboscis, or pharynx, into the digestive cavity which 

 has three chief branches one leading forward to the ante- 

 rior end of the body and two leading back on either side 

 of the mouth to the opposite end. The three main canals 

 have many small side pouches, and food is thus distributed 

 in the digestive system to all parts of the body. It is, 



