23S 



ZOOLOC4Y 



SECT. 



circ. ma* 



, mas 



ibi 



*5<4' x ^i 



outer surface. Internally, the interspaces between the organs 

 are filled by a peculiar form of connective-tissue, the paren- 

 chyma. 



Digestive System. -The mouth (Fig. 191) leads to a small 

 rounded bulb-like body, the pharynx (ph.), with thick muscular 

 walls and a small cavity. From this a short passage, the oesophagus, 

 opens into the intestine. The latter (int.) is frequently a very 



conspicuous structure, ow- 

 ing to its being filled with 

 the dark biliary matter 

 mixed with blood on which 

 the Fluke feeds. It divides 

 almost immediately into 

 two main limbs, right and 

 left, and from each of these 

 are given off, both inter- 

 nally and externally, a 

 number of blind branches 

 or ccsca, those on the inner 



FIG. 100. Fasciola hepatica. Section of the integu- side being short and Simple. 



meat, circ. nms. layer of circular muscular fibres: 1-1 ,n ,1 



cut. cuticle ; gl. unicellular glands ; long, nuts layer Willie tllOSC On tile OUtei 



^longitudinal muscular fibres jsp.spinutes. (After side are longer and 



branched. The two limbs 



of the intestine with their branches thus form, as in the Planarian, 

 a complicated system, the ramifications of which extend throughout 

 the whole of the body. There is no aperture of communication 

 between the intestine and the exterior, the only external opening 

 of the alimentary system being through the mouth. 



A branching system of vessels the water-vessels or vessels of 

 the excretory system ramify throughout the body. A longi- 

 tudinal main trunk opens behind by means of the excretory pore 

 already mentioned as occurring at the posterior end. In front it 

 gives of! four large trunks, each of which branches repeatedly, the 

 branches giving of? smaller vessels, and these again still smaller 

 twigs, until we reach a system of extremely fine microscopic vessels 

 or capillaries. Each of these ends internally in a slight enlarge- 

 ment situated in the interior of a large cell, an excretory cell or 

 flame-cell, similar to a flame-cell of the Planarian. 



The Liver-Fluke has a well differentiated nervous system, 

 which shares in the prevailing bilateral arrangement of the parts. 

 The central part of this system consists of a ring of nerve-matter 

 which surrounds the oesophagus and presents two lateral thicken- 

 ings, or ganglia, containing nerve-cells, and a single ganglion in the 

 middle line below. From this are given off a number of nerves, 

 of which the chief are a pair of lateral cords running back to the 

 posterior end and giving off numerous branches. There are no 

 organs of special sense. 



