PLANARIA FLEXILIS. 19 



nial, however, in so far as I have witness- 

 ed, except the planaria, actually sacrifices 

 its life to its inordinate appetite. 



These planarise dwell in society : they 

 are of an extremely pacific nature among 

 themselves, and very inactive, unless when 

 in pursuit of prey. Then they may be seen 

 traversing their element with a remarkable 

 motion, produced by the successive open- 

 ing and closing of the broad anterior part of 

 the body. They generally live half buried 

 in mud, a substance with which the vermes 

 and molluscse should constantly be provided, 

 particularly those undefended by any ex- 

 ternal covering ; but it should be pure and 

 unmixed with fragments of vegetable mat- 

 ter. The smoothness of its surface pecu- 

 liarly corresponds with the soft and deli- 

 cate texture of such creatures ; and they 

 should also be kept in glass vessels, as 

 earthen-ware, though fine in quality, is of- 

 ten too rough and unequal for them to pass 

 over, without suffering. A frequent change 

 of sea-water is beneficial, and it should al- 



