THE LIVER FLUKE 



119 



between the suckers is a smaller genital opening, at the hind end 

 of the body is a minute excretory pore, and on the dorsal surface 

 at about a third of the length of the animal from the front end 

 lies the opening of the Laurer-Stieda canal presently to be men- 

 tioned. The body is covered with 

 a cuticle, in which little back- 

 ward-pointing spinules are em- 

 bedded. 



GUT 



Mouth . 



Ventral sucker. 



Genital openinq. 



The mouth leads into an ovoid, 

 muscular pharynx, from which a 

 short oesophagus passes back- 

 wards to divide before the 

 posterior sucker into right and 

 left branches or intestines, which 

 run on either side of the middle 

 line to the hind end of the body, 

 giving off on either side many 

 offsets, which in turn are much 

 branched. There is no anus. The worm feeds largely on the blood of 

 its host, which is sucked from the wall of the duct, but probably 

 also on pieces of tissue rasped off by the sucker. It can also 

 absorb sugars, especially monosaccharides such as glucose and 

 fructose, through the general body surface. 



Fig. 83. — The Liver Fluke. 



LAYERS OF THE BODY 



The ectoderm cells have sunk inward after secreting the cuticle. 

 Below the cuticle lie successively circular, longitudinal, and 

 diagonal layers of muscle fibres, with the epidermal cells among 

 the longitudinal fibres (Fig. 84). Between these and the endo- 

 derm, which is a columnar epithelium hning the gut, lies the 

 parenchyma, a meshwork of protoplasm with nuclei at the 

 nodes and oval cells in the meshes. Muscle fibres pass across the 

 parenchyma from the dorsal to the ventral side of the body. 

 There are no blood vessels or coelom. It will be noticed that in 

 the fluke a mass of tissue hes between the ectoderm and endoderm 

 in place of the structureless lamella of Hydra. This is known as 

 the mesoderm. We shall allude to it in more detail in describing 

 the earthworm. 



