TREMATODA 



35 



CLASS II. TREMATODA 



The class Tremato'da is comprised of worms either internally 



or externally parasitic. The body is usually thicker than that 



^ of the turbellarians. The 



form is usually leaf-like, 





■-y ?; W 



Y\fr. 2'A. — 'I1ic common livor-Huke 

 (^V^s■^/'(;/(/ //,7«;/'/r,/ ) enlarged toshow 

 theaiiatomic <'liaract('r.s: ac, Aeetab- 

 uluni ; c, />., cirrus ])<)uch; I, intestinal 

 ceca; >/i, mouth with oral sucker; ov, 

 ovary; p. b., pharyngeal bulb; s. g., 

 shell gland; t, profusely branched 

 testicles; ut, uterus; va, vagina; 

 V. g., profusely branched vitcllogene 

 gland. (After Stiles, 1894, p. 300.) 



though it is sometimes elon- 

 gated. The anterior end is 

 distinguished by the arrange- 

 ment of suckers, and, in some 

 of the external parasites, by 

 eyes. 



Fig. 

 mon 



boring into a snail — x 370. 

 Thomas, 1883, p. 285.) 



The suckers are organs of adhesion and are sometimes armed 

 with })ristles or hooks. They are also used in locomotion, which 

 is a sort of looping, like that of the leech. Except in two cases 

 the vibratile cilia are not found on the surface. 



