454 Our Fresh-Water Planarice. 



ear-sliaped tentacles, are probably familiar to many sea-side 

 explorers, being not uncommon under stones, and within the 

 tangled roots of laminaria, but our business is with the fresh- 

 water, and not the marine species. 



The Planariaclce contain the species of true Planarice; 

 and, as I have already given my observations upon them, 

 there is no necessity to define the family again. It consists of 

 two genera, Polycelis and Planaria, the chief characteristic 

 distinctions between them being that Polycelis has numerous 

 oculiform spots of a black colour, bordering the anterior 

 margin of the animal ; these spots extend to about a third of 

 the length of the animal; whilst Planaria has two eyes, 

 nearly parallel, situated on the back of the head. 



Of the genus Polycelis, Dr. Johnston enumerates three 

 British species, viz : P. nigra, P. brunnea, and P. felina. The 

 two first are considered by some naturalists to be merely 

 varieties ; I am rather inclined to regard them as specifically 

 distinct. P. nigra is extremely common in ponds and ditches ; 

 it is evidently the " limace aquatique noire," portions of which 

 little creature Trembley used sometimes to treat his favourite 

 hydras with. The body is depressed, even, and very smooth ; 

 of a black velvet colour. Of an oval form when at rest : 

 linear-oblong when moving. The head is slightly sinuated 

 with a central projection in front, and two marginal ones : 

 this is seen only when the creature is in motion ; the oval 

 proboscis is long, white, and cylindrical, with a plain but 

 dilatable orifice ; length, when extended, about five lines, and 

 one and a half broad. 



P. brunnea does not differ, perceptibly, from P. nigra, 

 except in colour, which is a smoky-brown, with a dark mesial 

 line very distinct ; it is as common as the black species. 

 P. felina which, like the last named kind, is regarded by 

 Diesing only as a variety of P. nigra, is described as being 

 linear-oblong in form, minutely tricuspidate in front, of a 

 uniform dark brown, paler underneath, and eight lines long by 

 one and a half broad. I do not know the species ; it appears 

 to be the Planarian viganensis of Duges ; and from the decidedly 

 auricular form of the head, to judge from Duges figure, ought 

 perhaps, to be considered a distinct species. It inhabits 

 stagnant waters, in which aquatic vegetables abound, and 

 rarely is found in springs. Of the genus Planaria, Dr. Johnston 

 enumerates four British fresh- water species, viz : P. lactea, 

 P. torva, P. Arethusa, and P. Eclinensis. The first named species 

 is white or pinkish, and, shows most clearly the dendritic 

 cavity of the digestive system. When moving it is of an 

 oblong form, the front truncate, a little auricled on each side ; 

 but it assumes various forms, and frequently sinuates its 



