THE DENDROC(ELA. 



161 



known as Planarioe 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 lihabdoccela, 

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

 marine Planarim (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.—Polycelis {Lepfoplaira) Icevigata (after Quatrcfages).— a, month; b, buccal 

 cavity; c, oesophageal oriiice ; d, stoniacli ; e, raiiiific.ations of gastric caeca; /, 

 paii<;iia ; g, testes {h. vesiculse sennnales ; i, male t^euital canal ami peiiis ; k, ovi- 

 ducts ; /, spermatliecal dilatation at their junction ; m, vulva. 



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

 male aperture. Planaria dioica is unisexual. 



In some of the Planarlce there are distinct water-vascular 



