ANATOMY OF THE CESTODA 



289 



--C 



the cuticle. In the region of the septa the transverse and dorso- 

 ventral muscles form a kind of plate. 



The mass of parenchyma bounded by the transverse muscles is 

 termed the MEDULLARY layer, while the mass lying outside them 

 is termed the CORTICAL LAYER. 



It was known long ago that the myoblasts adhere to the dorso- 

 ventral fibres as thickenings, but it is only recently that large star- 

 shaped cells (fig. 184), separated from but connected with them by 

 processes, have been recognized as 

 the myoblasts of other fibres (Bloch- 

 mann, Zernecke). 



Within the scolex the direction 

 and course of the muscular layers 

 change. 



The SUCKERS are parts of the 

 musculature, locally transformed, 

 with a powerful development of 

 the (torso-ventral muscles, now 

 become radial fibres. 



The ROSTELLUM of the armed 

 Taeniae, like the proboscis of the 

 Rhynchobothriidcc, also belongs to 

 the same category of organs. 



In the simplest form, the ros- 

 tellum, or top of the head (as 

 in Dipvlidium caninum), appears 

 as a hollow oval sac, the anterior 

 part of which, projecting beyond 

 the upper surface of the head, carries several rows of hooks (fig. 186). 

 The entire internal space of the sac is occupied by an elastic, slightly 

 fibrous mass, while the anterior half of the surface of the rostellum is 

 covered by longitudinal fibres and the posterior half by circular fibres. 

 On contraction of the latter the entire mass is protruded through the 

 apical aperture, the surface of the rostellum becomes more arched, and 

 the position of the hooks is, in consequence, altered. The rostellum 

 of the large-hooked Tceniida, which inhabit the intestine of man and 

 beasts of prey, is of a far more complicated structure, for, in addition 

 to the somewhat lens-shaped rostellum carrying the hooks on its outer 

 surface, there are secondary muscles grouped in a cup-like manner 

 (fig. 187). Every change in the curvature of the surface of the rostellum 

 induces an alteration in the position of the hooks. In the hookless 

 Tczniida the muscular system of the rostellum is altered in a very 

 different manner ; in a few forms a typical sucker appears in its place. 

 The NERVOUS SYSTEM commences in the scolex and runs through 

 19 



FIG. 1 86. Dipylidium caninum : from 

 the cat. In the upper figure the rostellum is 

 retracted, in the lower protruded, a, sucker ; 

 , hooks of rostellum ; , enlarged hook ; 

 c, apical aperture on scolex ; d, longitu- 

 dinal muscles ; e, circular muscle?. (After 

 Benham.) 



