2I 4 



THE ANIMAL PARASITES OF MAN 



and the originally flat cell walls become transformed into trabeculae. 

 According to this view the cavities filled with fluid are infra-cellular, 

 according to the former view inter-cellular. Pigment cells occur only 

 in a few species. 



The MUSCULAR SYSTEM of the Trematodes is composed of (i) a 

 dermo-muscular tube, (2) the dorso-ventral or parenchymal muscles, 

 (3) the suckers, and (4) the special muscles of certain organs. 



The dermo-muscular tube, which lies fairly close to the cuticle, 

 consists of annular, diagonal, and longitudinal fibres which surround 

 the entire body in one or several layers, and as a rule are more strongly 

 developed on the ventral surface as well as in the anterior part of the 

 body. The MUSCLES OF THE PARENCHYMA are found chiefly in the 



7. 



Md. 



F.v.s. Cu- 



F.v.s. ..,.. 



Ex.v. 



FIG. 120. Half of a transverse section through Fasciola hepatica, L. 25/1. Cu., Cuticle 

 with scales; under the cuticle are circular muscles, and adjoining them the longitudinal and 

 diagonal muscles; internal to the latter are the matrix cells of the cuticle; /., gut; the 

 other similarly contoured cavities are gut diverticula that have been transversely or obliquely 

 sectioned; F.v.s., vitellaria ; Ex.v., excretory vessels; T. y testes ; Md., median plane; the 

 fibres passing from the ventral to the dorsal surface are the muscles of the parenchyma. The 

 parenchyma itself is omitted. 



lateral parts of the body and pass through the parenchyma in a 

 dorso-ventral direction ; their diverging brush-like ends are inserted on 

 the inner surface of the cuticle (fig. 120). 



The suckers are specially differentiated parts of the dermo- 

 muscular tube. Their concave inner surface is lined by the con- 

 tinuation of the cuticle and their convex external surface is covered 

 by a more dense tissue that frequently takes the form of a refractive 

 membrane, thus separating them from the parenchymal muscles. 



The principal mass of the suckers consists of muscular fibres which 

 run in three directions equatorial, meridional and radial. The 

 equatorial fibres correspond to the annular muscles, the meridional 

 fibres to the longitudinal muscles, and the radial fibres to the muscles 

 of the parenchyma; the radial fibres are always the most strongly 



