PHYLUM PLATYHELMIXTHES 



227 



disposed muscular fibres (circ. mits. ): (3) a layer of longitudinal 

 muscular fibres (lomj. /////*.). A cellular epidermis is \\anting. 

 Beneath the muscles are numerous unicellular glands (///.), the 

 ducts of which, in the form of processes of the cells, open on the 



FIG. 17(>. Distomum hepaticum. Section "f the integument, circ. mus. layer nt circular 

 muscular fibres ; re/, cuticle ; <il. unicellular glands ; lout/, nuts, layer of longitudinal 

 muscular fibres ; xji. spiiiulcs. (After Br.um.) 



outer surface. Internally, the interspaces between the organs are 

 filled by a peculiar form of connective-tissue, the parenchyma. 



Digestive System. The mouth (Fig. 177) leads to a small 

 rounded bulb-like body, the pliar/in > (/'//.), with thick muscular 

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

 leads to the intestine. The latter (int.) is frequently a very 

 conspicuous structure, owing to its being filled with the dark 

 biliary matter on which the Fluke feeds. It divides almost imme- 

 diately into two main limbs, right and left, and from each of 

 these are given off, both internally and externally, a number of 

 blind branches or cwea, those on the inner side being short and 

 simple, while those on the outer 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 off four large trunks, each of which branches repeatedly, the 

 branches giving off 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 the flame-cells of the Planarian. 



Q 2 



