STRUCTURE AND ARRANGEMENT OF THE SUCKERS. 395 



is filled with the same clear connective substance which we have 

 already observed inside the rostellum. 



A similar arrangement is to be observed in the Cystotcenim 

 (Fig. 234), only that here the muscles both of the outer sac and 

 of the rostellum are considerably thickened at the expense of the 

 inner space. Eostellum and sac, therefore, appear as almost solid 

 muscular masses, whose true nature is all the more readily over- 

 looked, since, in their flattened character and external configuration, 

 they differ from the above described extended proboscis -like appar- 

 atus. We shall afterwards return to their discussion. 



Like the rostellum, the suckers of the Taeniadae are organs which, 

 by the development of a homogeneous boundary sheath, are sharply dis- 

 tinguished from the surrounding body-parenchyma, and therefore 

 acquire a certain anatomical independence. All the four lie, of 

 course, at the same height, in the equatorial line where the head 

 is broadest, and are, in spite of their depth, usually entirely 

 buried in the substance of the head, so that only their borders project. 

 According to the height of these projections, the head appears 

 more or less quadrangular. The corners represent in position the 

 lateral borders of the body, and so far repeat even its flattened char- 

 acter, since the intervals separating the suckers are greatest where 



FIG. 231. Apical surface and circle of hooks in Tcenia solium. ( x 80.) 



they correspond to the surfaces of the body. We need hardly mention 

 that the suckers in the various species vary widely both in relative 

 and absolute size. The strength of the musculature differs also widely, 

 thus, of course, affecting the fixing power of the worms. The arrange- 

 ment of the fibres, however, is on the whole uniform throughout, as 

 was to be expected from the uniformity of the action performed. x 



1 [Quite recently the structure of the suckers in the Taeniadse, as well as in other 

 groups of animals, has been made the subject of a special treatise : Niemiec, " Recherches 

 microscopiques sur les ventouses," Rec. zool. suisse, t. ii., p, i., 1885. R. L.] 



