56 



PLATYHELMINTHES TREMATODA 



CHAP. 



todes. The blood and epithelia of the host are sucked, and to 

 this end the pharynx has frequently a chitinous armature to aid 

 in the abrasion or inflammation of the tissues upon which the 

 parasite feeds. In the case of a Sturgeon attacked by JVitzschia 

 elongata, a Tristomid, the mouth of the host appeared to be 

 highly inflamed by these attacks (v. Baer). 



The suckers, in the two families under consideration, vary 



in number and complexity. There 

 is always a powerful apparatus at 

 the hinder end of the body secur- 

 ing the Trematode firmly to the 

 slimy body or gills of its host, and, 

 usually in the Polystomatidae, a 

 pair of suckers at the sides of the 

 mouth accessory to the pumping 

 action of the pharynx. In Axine, 

 and to a less extent in Octo- 

 hothrium (Fig. 23), the suckers 

 are strengthened by a complex 

 hingework of chitinoid bars or 

 hooks, which serve as insertions 

 for the muscles of the suckers, 

 and thus increase their efficiency. 

 The mouth is invariably pre- 

 sent just beneath the anterior end of 

 the body. It leads into a muscular, 

 pumping pharynx (Fig. 24, ph), 

 and this into a bifurcated intes- 

 tine which ends blindly. The 

 two openings of the excretory 

 system lie on the dorsal surface 

 (as in Temnocephala), and the 

 excretory canals branch through 

 the substance of the body, ending usually in " flame-cells." The 

 nervous system is highly developed, and resembles that of Temno- 

 cephala (Fig. 21) in detail. Upon the brain one or even two pairs 

 of eye-spots are present in the larvae, and may persist throughout 

 life. Tactile setae occur in Sphyranura, a parasite of the North 

 American Amphibian JYecturus, but a cellular epidermis is 

 apparently rendered impossible, perhaps from the nature of 



Fig. 23. Octobothrium merlangi Kuhn, 

 from the gills of the whiting. x 

 8. int, Intestine ; ms, mouth ; sc 

 suckers with chitinoid armature ; yk 

 yolk-glands. (After v. Nordmann.) 



