THE DENDROCCELA. 



161 



known as Planarim belong to this division. Some are ma- 

 rine, some fresh-water, and some terrestrial. 



In the fresh-water forms, the female reproductive appa- 

 ratus has a distinct vitellarium, as in the higher Hhabdocoela, 

 and there is only one common genital aperture. But, in the 

 marine Planariaz (Fig. 33), there is no vitellarium ; the ova- 

 ries and testes are numerous, and scattered through the meso- 

 derm, being connected with the exterior by ramifications of 

 the oviducts and of the vasa deferentia. A ramified gland, 

 which secretes a viscid albumen or envelope for the eggs, 



Fig. 33.—Polycelis (Leptoplana) laevigata (after Quatrefage?).— a, mouth; £>, buccal 

 cavity; c, oesophageal orifice ; d, stomach ; <?, ramifications of gastric caeca; /", 

 ganglia; g, testes; A, vesiculse seminales; i, male genital canal and penis ; k, ovi- 

 ducts ; I, spermathecal dilatation at tbeir junction ; m, vulva. 



opens into the vagina, and the female is distinct from the 

 male aperture. Planar ia dioica is unisexual. 



In some of the Planarioe there are distinct water-vascular 



