240 



ZOOLOGY 



SECT. 



par 



eel 



cere, mus 



Itvt long.mus 



dors vent, mus 



o.d ™ 



I'ii;. IS"). — Transverse section of a Planarian. rirc. mm*, circular muscular fibres ; coec. in- 

 testinal ca;ca ; dors. vent. mus. dorso- ventral muscular fibres ; ect. ectoderm ; ext. long. mus. 

 external layer of longitudinal muscular fibres ; int. central lumen of the intestine ; int. long, 

 mus. internal layer of longitudinal muscular fibres ; nc. nerve-cords ; o. <!. oviducts ; par. 

 parenchyma ; test, testes ; v. def. vas deferens ; vit. vitelline glands. (From Hatschek's 

 Lihrbuch.) 



ii. The Liver-Fluke (Fasciola hepatica). 



General Features. — The Liver-Fluke 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-lobe, projecting from the 

 broader end. The symmetry 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 spinulcs 

 or papillae, 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 sucker. A short distance back 

 on the ventral surface, just behind the head- 

 lobe, is a second much larger posterior sucker (sckr.). Between 

 the two suckers, but rather nearer the posterior one, is a 

 median aperture, 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.). 



excr 



Fig. lSt>. — F asciola 

 hepatica, natural 

 size. excr. excretory 

 pore ; mo. mouth \repr. 

 reproductive aperture; 

 sckr. posterior sucker. 



