PLANARIA NIGRA. 23 



sects, infinitely survive the term which we 

 generally conceive appropriated to them. 

 It is accident that abridges life ; seldom the 

 simple decay of nature. 



Planaria Nigra, Fig. ^3. 5. 15. During 

 the sunshine of summer, a small jet black 

 velvet-skinned animal may be often seen 

 crawling near the edge of fresh-water ponds 

 and ditches, with a lively, smooth, and glid- 

 ing motion. This is the Black Planaria, 

 which has already been characterized and 

 described by different naturalists ; but, un- 

 fortunately for that accuracy which should 

 mark the progress of science, their superfi- 

 cial observations concerning it have led to 

 those numerous errors which darken the 

 history of the whole genus. 



Sometimes it is found in slow running 

 waters, and there of the largest size, but 

 usually when they are almost stagnant, 

 and, in particular, where aquatic plants 

 abound. On these, numbers crowd toge- 

 ther as the colder season advances, each 



