16 PLANARIA FLEXILIS 



has actually been received, reach from the 

 center to the margin. 



Planariae, in the natural state, perhaps 

 feed on the mucilaginous parts of vegeta- 

 bles ; they are likewise carnivorous in the 

 highest degree, greedily devouring animal 

 substances, particularly the softer kinds, as 

 mussels, oysters, and others of the mollusca 

 tribes. Unless a certain temperature pre- 

 vail, all aliment is rejected ; and when the 

 thermometer stood at 45, with chill winds, 

 it has been necessary to remove them to a 

 warmer atmosphere, where they readily fed. 

 Nevertheless, they sometimes refuse food 

 for weeks together, though in a favourable 

 situation. Their voracity is incredible : 

 the whole flexile body is employed in firm- 

 ly infolding the prey : if living, its Strug- 

 gles are vain to get free ; it is gradually 

 absorbed, until the capacity of the viscera 

 can receive no more. But, contrary to 

 what is witnessed in other animals, of which 

 the belly protrudes with repletion, the back 

 of the planaria rises in proportion to the 



