32 PLANARIA NIGRA. 



portion to the violence offered to its other- 

 wise dehcate frame. It may almost be 

 called immortal under the edge of the knife. 

 Innumerable sections of the body all be- 

 come complete and perfect animals : if the 

 head be cut off, a new head replaces it : 

 if the tail be severed, a new tail is acqui- 

 red : nay, if one half of the whole animal 

 be longitudinally separated from the other, 

 the defective portion is speedily repaired. 



A grand and leading law of nature is in- 

 variably to fulfd her original object ; whence 

 we must conclude, that the permanence of 

 accidental lacerations, which we occasion- 

 ally witness, results from some unknown 

 condition opposing the progress of repro- 

 duction. In the artificial mutilations, 

 whose advances can be watched, the pe- 

 riod of renewal is strictly commensurate 

 with the temperature of the atmosphere. 

 Regeneration is retarded, or altogether sus- 

 pended, by the cold of winter ; promoted 

 by the heat of summer; and still further ac- 

 celerated by augmenting the natural 



