236 PLATYHELMINTHES. 



Pliyllocotyle Ben. and Hesse ; Hexncotyle Blainv. ; Platycotylc Ben. and 

 Hesse ; Plcctanocotylc Dies. 



Sub-fam. 2. Polystomidae. Without oral suckers and larger genital 

 hooks. Adhesive disc usually with 6 suckers, and with hooks. On 

 the gills of m. fishes, on the skin, gills, or in the bladder of Amphibia or 

 Reptiles. Polystonuim (Fig. 185) Zeder ; Onchocotyle Dies. ; Erpocotylc 

 Ben. and Hesse ; Diplobothrium Leuck.; Sphyranura R. Wright. 



Sub-fam. 3. Microcotylidae. With two oral suckers, and with genital 

 hooks. Adhesive disc with numerous suckers. On gills of m. fishes. 

 Microcotylc Ben. and Hesse ; Gastrocotylc Ben. and Hesse ; Axine Abildgaard ; 

 Pseudaxine Par. and Per. 



Sub-fam. 4. Gyrodactylidae. Usually without oral suckers. Anterior 

 end with 2 or 4 cephalic lappets, or with sucker-like membrane ; excretory 

 organs opening at the hind end ; adhesive disc usually with small radially 

 arranged hooks, and 2 or 4 larger central hooks, without suckers. Repro- 

 duction by eggs which are either laid, or develop within the mother into 

 a young form which may itself produce a second generation while still in 

 the parent, v. Siebold believed that he had observed a young animal 

 developing from a germ-cell of Gfyroductylas, and that this became pregnant 

 during its development. He regarded the Gyrodaciylus as an asexual form 

 since he failed to find organs for the production of sperm. G. Wagener, 

 however, showed that the reproduction is sexual, and conceived the idea 

 that the germs from which the second and third generations are formed are 

 derived from the remains of the fertilized ovum, from which the first 

 generation is formed. Metschnikoff too is of the opinion that the individuals 

 of the first and second generations are formed at the same time from a 

 common mass of similar embryonic cells. On gills or integument of fishes. 

 Calceostoma Ben. and Hesse ; Gyrodactylus v. Xordm., G. elegans v. Nordm., 

 from the gills of Cyprinoids and f.w. fishes ; Dactylogyrus Dies.; Tetraonchus 

 Dies. ; Amphibdella Chatin ; Diplectanum Dies. 



Order 2. ASPIDOCOTYLEA. 



Body very variously shaped. Adhesive apparatus ventral, large, 

 round, oval, or elongated, more or less distinctly marked off from the 

 body, and possessing numerous suckers arranged in one or several 

 rows, without armature. Mouth terminal or sub-terminal without 

 oral sucker; oesophagus short, with a more or less developed pharynx; 

 intestine saccular. Genital pore median, ventral, anterior to adhesive 

 organ ; penis sheath opens into widened end of uterus, which is 

 much coiled ; usually one testis ; Laurer's canal absent ; yolk-gland 

 paired. Eggs without filaments. Excretory organs open posteriorly 

 by one, somewhat dorsally placed, pore. Development direct with 

 simple metamorphosis. A ciliated covering is not developed during 

 the embryonic development. Parasitic in the alimentary canal 

 and gall bladder in Chelonia and fishes, and in different organs 

 in Molluscs. 



