MANUAL OF ELEMENTARY ZOOLOGY 



Gut, 



tines, 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 on the juices, probably 



normally on the blood, 

 of its host. 



The so-called cuticle is 

 a horny layer 

 Wo& formed by 

 the transfor- 

 mation of the epidermis 

 or ectoderm (Fig. 404). 

 Below it lie successively 

 circular, longitudinal, 

 and diagonal layers of 

 muscle fibres. Between 

 these and the endoderm, 

 which is a columnar 

 epithelium lining the 

 gut, lies the parenchyma, 

 a meshwork of proto- 

 plasm 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 ccelom. It will be 

 noticed that in the 

 fluke a mass of tissue 

 lies between the ecto- 

 derm and endoderm in 



Fig. 1 22. — The structure of a liver fluke. 

 — After Sommer. From the ventral 

 surface. The branched gut (g. ) and place of the Structure- 

 the lateral nerve (l.n. ) are shown to 

 the left of the figure, the branches 

 of the excretory vessel (e.v. ) to the 

 right. 



, Position of cirrus sac; g:, lateral head 

 ganfilion ; w., month ; ph., pharynx ; v.s., 

 ventral sucker. An arrow indicates the 

 excretory aperture, 



less lamella of Hydra. 

 This is known as the 

 mesoderm. We shall 

 allude to it in more 

 detail in describing the 

 earthworm. 



