THE DENDROC(ELA. 



161 



known as Planari(B 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 Hhahdocoela^ 

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

 marine PlanaricB (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. SS.—Poli/cdis {Leptoplana) laevigata (after Quatrefages).— a, mouth; 6, buccal 

 cavity; c, oesophageal orifice ; d, stomach ; f, ramifications of gastric caeca; f, 

 ganglia; g, testes; h, vesiculae seminales; i, male genital canal and penis ; k, ovi- 

 ducts ; I, spermathecal dilatation at their junction ; ?», vulva. 



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

 male aperture. Planar ia dloica is unisexual. 



In some of the Planarim there are distinct water-vascular 



