24(1 



ZOOLOGY 





dors ver.t nuie 



od 



Fig. Is'). — Transverse soetion of a Flanarian. rirc. riius. circular muscular fibres; ccec. in- 

 testinal ca;ca ; dors, reii,t. runs, dorso-ventral muscular fibres ; t^cf. ectoderhi ; ej:f. lonci. vius. 

 external layer of longitudinal muscular fibres ; int. centr.vl lumen of the intestine ; iiit. long. 

 ',}ivs. internal layer of longitudinal muscular fibres ; ae. nerve-cord.s ; o. d. oviducts ; ■par. 

 parenchyma ; tt^sf. testes ; v. def. vas deferens ; vit. vitelline glands. (From Hatschek's 

 Linirhucll'.y 



ii. The Liver-Fluke (Fasciola hcpatica). 



General Features. — The Liver-Fhike of the Sheep, which is to 

 be found in the interior of the larger bile-ducts of the infested 

 animal, is a soft-bodied worm of flattened leaf-like shape (Fig. 

 186), with a triangular process, the head-lohe, projecting from the 

 broader end. The symmetrj' of the parts is 

 distinctly bilateral, as in the Planarian. Ex- 

 ternally the body is quite equilateral, the right 

 and left portions exactly balancing one another, 

 but, as will appear subsequently, this complete 

 symmetry does not extend to all the internal 

 organs. 



The surface is devoid of vibratile cilia, but 

 is covered with innumerable minute spinules 

 or paioillm, which are prolongations of the 

 homogeneous external layer or cuticle investing 

 the whole animal. At the extreme anterior 

 end of the triangular head-lobe is the small 

 opening of the mouth {mo.) surrounded by a 

 muscular oral sticlcer. A short distance back 

 on the ventral surface, just behind the head- 

 much larger posterior sucker (sch:). Between 

 but rather nearer the posterior one, is a 

 the genital opening (rcpr.), through which a 

 curved muscular process, the cirrus or penis may be protruded. In 

 the middle of the posterior end of the body is a minute opening, 

 the excretory pore (excr.). 



FiQ. 186.— r a s c i o 1 a 

 hepatica, natural 

 size. excr. excretory 

 pore ; mo.jnouth ; repr. 

 reproductive aperture; 

 sch: posterior sucker. 



lobe, is a second 

 the two suckers, 

 median aperture, 



