52 



YEEMES. 



Catenulidce. 

 Catenula. 



DENDROC(ELA. 

 Planariidce. 

 Polycelis. 

 Planaria. 



Geoplanidce. 

 Bipaliurn. 

 G-eoplana. 

 Polycladus. 



Euryleptida. 

 Stylochus. 



Planocera. Lineidte. 



Leptoplana. Lineus- 



Thysanozoon. Borlasia. 



Cephalolepta. Meckelia. 



Eurylepta. Micrura. 



EHYNCHOCCELA. Amphi p ri d(S 



Cepkalothricida. Nemertes. 



Cephalothrix. Tetrastemma. 



Ommatoplea. Amphiporus. 



Carinellidce. 



CarineUa. Pelagonemertes. 



Valencinia=Polia. Pterosoma. 



Balanoglossus. 



Order II. TBEMATODA. 



External or internal parasites, flattened or rounded, not ciliated 

 in the adult state, and provided with one, two, or more ventral 

 suckers. Mouth and anus in one. Mostly hermaphrodite. 



The alimentary canal lies in the substance of the body, and not 

 in a free perivisceral space ; in a few it disappears in the adult, 

 and is sometimes much branched. 



Some of these parasites scarcely undergo any change [Mono- 

 genea] ; others [Digenea] begin life on leaving the egg as a free 

 ciliated infusorian ; if it meets with a suitable host in its wander- 

 ing, it puts on many forms before reaching maturity. Individuals 

 proceeding from ciliated embryos also produce buds which deve- 

 lop numerous tadpole-shaped larvae [cereariae], which, when their 

 ciliated skin has been thrown oif, are known as " redise." Cer- 

 cariae often become encysted ; and in that state they are said to 

 wait for years before their host is swallowed by the creature in- 

 tended to lodge them. The cyst is then broken up, and the worm 

 is set free to begin another form of life. 



These parasites, of which there are about 500 species, are found 

 on the gills and skin of fishes, on mollusks, Crustacea, &c., and in 

 the eyes, blood-vessels, and intestines of man and other animals. 

 Distoma hepaticum is the liver-fluke of sheep. In Bilharzia 

 hcematobi'iis, common in the Egyptians, the slender female is 

 lodged in an abdominal groove of the larger and stouter male. 



