130 THE ANIMAL PARASITES OF MAN 



dorsum ; usually also the beginning of the intestine is surrounded 

 by a sucker. 



Tn or near the suctorial apparatus there are chitinous hooks, 

 claws or claspers, or the surface of the body is more or less 

 covered with spines, scales or prickles ; in one species (Rhop alias) 

 there is a projectile rostrum beset with spines. 



The body of all the Trematodes is covered by a homogenous 

 CUTICLE of varying thickness, which either lies directly over the 

 external layer of the p'arenchyma, which is thickened into a kind 

 of basement membrane, or is situated immediately over the 

 muscles embedded in the parenchyma. The pyriform or fusiform 

 EPITHELIAL CELLS lie in groups with their thickest parts between 

 or directed towards the internal of the diagonal muscles, but a 

 process directed outwards also connects them with the basal 

 surface of the cuticle. There are also unicellular cuticular glands, 

 lying isolated or in groups, which are termed head, abdominal, or 

 dorsal glands according to the position of their orifice. 



.THE PARENCHYMA is a connective substance, i.e., it consists of 

 numerous multipolar cells, the offshoots from which branch strongly, 

 then anastomose with each other as well as with the offshoots of 

 other cells, so that a network, permeating the entire body and 

 encompassing all the organs, is produced. There is in addition a 

 homogenous matrix, in the form of lamellae and trabeculae, that 

 border small cavities communicating with each other and filled with 

 a liquid substance. 1 In some species the parenchyma encloses 

 pigment cells. 



The MUSCULAR SYSTEM of the Trematodes is composed of a 

 musculo-dermal tube, the dorso- ventral or parenchj/mal muscles, the 

 suctorial discs, and the special muscles of certain organs. 



The musculo-dermal tube, which lies fairly close to the cuticle, 

 consists of annular, transverse, 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 lateral parts of the body and pass through 



1 According to other authors, the parenchyma of the Trematodes consists originally 

 of similar cells, of which, however, in the adult stage, only the cellular membranes 

 have remained, between which an intercellular mass has appeared, while the proto- 

 plasm has been transformed into a watery liquid in which only here and there a nucleus, 

 surrounded by a little unaltered protoplasm, has remained. By partial absorption 

 of the walls contiguous spaces become connected, and their originally flat partitions 

 become trabeculae. 



