FIELD BOOK OF PONDS AND STREAMS 



and then sucks the food through it (Fig. 93, i). At other 

 times it is pulled back into the body through an opening on 

 the under side (Fig. 93, 2). This is visible only from beneath 

 or when a planarian glides upside down under the surface film 

 of the water. Food sucked in through the pharynx goes into 

 the large more or less branched intestine, which often shows as 



Fig. 93. — Common planarians: i, upper surface 

 showing the ear-like auricles and the eyes, the 

 cylindric pharynx thrust out from the body as in 

 feeding ; 2, diagram of planarian showing its branched 

 food canal and the pharynx pulled back into its 

 sheath within the body. 



a vinelike tracery on the backs of planarians. It has only one 

 opening and the waste must go out through the mouth just as 

 it does in Hydra. 



Planarians are very sensitive to the conditions around them. 

 They appear uncomfortable in bright light, and will try to get 

 into a shadow or into the dark, in the meantime keenly dis- 

 criminating between small differences in the light. They 

 are responsive to very slight vibrations, especially sensitive 

 to temperature, and must have a sense of taste for they are 

 soon attracted to a crushed snail or any meat juice in the 

 water. With rare exceptions they are hermaphroditic, each 

 animal having a complete male and female reproductive 

 system. Most of them produce thin-shelled transparent 

 summer eggs as well as the thick-shelled winter eggs or 

 "cocoons." But though they are equipped with this elabor- 

 ate reproductive machinery, all turbellarians depend upon the 



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