TREMATODA MONOGENEA 



55 



In habits, in the character of the skin, the mnscular, digestive, and 

 reproductive systems, they find their nearest allies in Ehabdocoels 

 (Vorticidae). But in the excretory and nervous systems, the 

 latter composed of two dorsal, two lateral, and two ventral trunks 

 all connected together (Fig. 21), they are Tristomid Trematodes. 

 Thus they may fitly connect an account of the two great groups. 

 II. Tristomatidae and III. Polystomatidae} The members of 

 these families are found on the body, or attached to the gills, of 



Fig. 22. A, Nematobothrium 

 JUarina van Bened. Nat. 

 size. Two individuals [a and 

 b) are found together, encysted 

 on the branchial chamber of 

 the Tunny. B, UdoneUa call- 

 gorum Johns. A Tristomid, 

 several of which are attached 

 to the ovary of a Copepod 

 (Caligus), itself a parasite on 

 the gills of the Hake, x 8. 

 C, Epibdella hippoglossi 

 0. F. M. A Tristomid found 

 on the body of the Halibut. 

 Nat. size, m, Mouth ; rru, 

 lateral suckers ; ov, ovary ; ps, 

 posterior sucker ; te, testes. 

 (All after P. J. van Beneden.) 



fresh-water and marine fishes. The edible and inedible fish of 

 our coasts have each their particular ectoparasitic Trematodes ; 

 while the Minnows, Sticklebacks, and Miller's Thumbs of streams 

 and ponds are attacked by Diplozoon, Gyrodactylus, and other 

 forms. The aquatic Amphibia also harbour a number. Polystom u m 

 integerrimum is common in the bladder of Frogs, where it leads 

 a practically aquatic life. Other species of Polystomum inhabit 

 the buccal and nasal cavities of certain Chelonia, but naturally 

 no terrestrial Vertebrates are infested externally by these Tivnia- 



1 Braun, in Bronn's Klassen it. Ordn. d. Thicrrcichs, vol. iv. p. 407, gives a valu- 

 able summary of our knowledge of this group. For figures, see van Beneden and 

 Hesse, Mdmoircs de V Acad. roy. dc Bclgiquc, torn, xxxiv. 1864, pp. 1-169. A 

 valuable paper (with synoptic tables) on Japanese Monogenea, by Goto, Journ. 

 Coll Sci. Japan, vol. viii. pt. 1, 1894, has recently appeared. 



