PHYLUM PLATYHELMINTHES 

 132 



Order Tricladida. in which the gut has three main branches. 

 Demlrocaliun lackiim, Planaria lugnbris and Polycehs nigra are 

 all found HI ponds and slow streams ; the first is white, and the 

 other two black, but Poly eel is has an anterior rmg of eyes by 



'y- 9.0. 





ph.s. 



Fig. 95.— a turbcUarian {Planaria polychroa) .—From Shipley and MacBride. 

 csl CiliAted sensory slit at side of head ; eye ; g.o.. genital opening ; m., rnouth. at end of outstretched 

 CM., cuiaiea sen^ > pharynx ; ph.s., sheath into which pharynx can be withdrawn. 



which it may be recognised. Planaria alpina, also black, is found 

 in mountain streams. Procerodes litoralis {■=Gunda hIvcb) is marine 

 and is found in rock pools. Some species are terrestrial. 



CLASS II—TREMATODA 



These are parasitic, or rarely epizoic. They have a thick cuticle, 

 and suckers, and the adult has no external ciha. Fasciola is 

 characteristic of the class, though its genital organs are more 

 complicated than those of most species. 



CLASS III—CESTODA 



The tapeworms are entirely endoparasitic. There is no gut, 

 and the ectoderm cells have sunk into the parenchyma, leaving a 

 thick cuticle at the surface. CiUa are absent except for the flame- 

 cells. The characteristic form of the body of the adult is that with 

 scolex and proglottides as shown by Tcenia solium. 



Other common tapeworms are : Tcenia saginata, without hooks, 

 found in man, with the bladder-worm stage in the ox ; it may be 

 up to forty feet, or occasionally eighty feet long, and may have 

 2000 proglottides ; T. serrata in the dog, with a bladder-worm in 

 rabbits, hares, and mice ; T. coenurus in the dog, with the bladder- 

 worm known as Ccenurus cerebralis in the brain of sheep and 

 other hoofed animals, where it causes ' staggers ' ; and T. 

 echinococcus, which has only three proglottides, in the dog, with 

 the bladder-worm Echinococcus in sheep, oxen, pigs, and some- 



