TTREELLABIA DENDROCCELA. 



315 



probably the function of tactile organs. The mouth usually lies 

 in the middle of the body, and leads into a wide and protrusible 

 pharynx. The skin is often provided with glands, the secretion 

 of which in certain land Planaria (Bipalium, Rhynchodesmus) 

 hardens to a fibrous web. They are almost always hermaphrodite. 

 The fresh-water forms possess a common 

 generative opening, while in the marine 

 forms the generative openings are usu- 

 ally separate (fig. 250). In the latter 

 case a separate vitellariurn is absent. 

 In some marine forms development 

 takes place with metamorphosis, as is 

 shown by the larva discovered by J. 

 M tiller, which possessed six provisional 

 finger-like ciliated lobes (fig. 251). 

 In the fresh- water Planarians develop- 

 ment is direct. The cocoon, when laid, 

 contains four to six small eggs. At the 

 close of segmentation there is developed 

 a layer of cells, which is said to split 



into two layers, an upper or animal layer, from which are derived 

 the body wall and muscular system, and a lower or vegetative, from 

 which the alimentary canal is formed. The marine Dendroccela fre- 

 quently deposit their eggs in the form, of broad bands. 



1. Monogonopora Stimps. Den- 

 droccda with single sexual opening. 

 The land and fresh-water Planaria be- 

 long to this group. 



FIG. 251. Larva of Eiirylepta auri- 

 culatd after Hallcz. 



i 



c 



a 



FIG. 252. Planaria potycJiroa (), 

 lugulris (4), torva (c), about twice 

 the natural size (after O. 

 Schmidt). 



Fam. Planariadse. The body is of a long, 

 oval, flattened shape, and is often provided 

 with lobed processes, more rarely with ten- 

 tacles, and, as a rule, with two eyes, which 

 are provided with lenses. Planaria 0. Fr. 

 Muller, two eyes, no tentacles. PL torra, 

 M. Sch. (divided by 0. Schmidt into 

 2>oli/chrou, and torvu') (fig. 2o2). PL 

 Clap., with separate sexes. J)r>iih-i>etrliim 

 Oer.st. Distinguished by the possession of 

 lobed processes on the head, also by the 



presence of a copulatory organ placed in a special sheath. D. Indciim Oerst., 



Polycelis n'ujra. bntnnea O. Fr. Mull. 



Fain. Geoplanidae.* Land Hanarians. They are characterised by their 



* Besides 31. Schultze, Stimpson, Mctschnikoff, Grube, etc., compare II. N. 



