NEW CHSTODES FROM THE TASMANIAN DEVIL. 683 



upon the scolex. The structure of the sucker is not like that of 

 the typical Tetracotylean sucker. In the latter there is one thick 

 layer of typically arranged muscle-fibres (into the nature of which 

 arrangement it is not my purpose to enter^it is well known) 

 which is quite distinct from the surrounding tissues of the scolex, 

 but never covei-ed by them on its free sui^face, which faces towards 

 the aperture. In the present species the structure of this sucker 

 is illustrated in the accompanying text-figure (text-fig. 96), which 

 is drawn from one sucker only which appears to me to be rather 

 larger than its fellow, the two being thus mutually asymmetrical. 

 Examining the sections from below upwards, the sucker is seen 

 at first to be apparently like that of the Tetracotylea generally. 

 It consists of a strongly marked layer of muscle-fibres etc. lying 

 in a cavity of the body parenchyma. This is shown in the 

 figure. As we approach more nearly to the rostellar region, 

 another layer in which the hooks are implanted pushes itself 

 in front of the sucker proper, as is also shown in the text- 

 figure referred to. This layer is continuous with and similar 

 in structure to the general parenchyma of the head. The 

 true (?) sucker thus gets as it were buried beneath a layer 

 of tissue bearing hooks. So far the structure of this sucker 

 will be plain from the sections figured. In the corresponding 

 sucker of the opposite side of the body the hooks are obvious 

 and quite similar, and imbedded in a perfectly corresponding 

 tissue. Bat I could find no trace whatever of the muscular 

 structure independent of these hooks. 



In addition to these two suckers the scolex of Dasyurotcenia 

 possesses two others, thus making the normal four. The latter 

 are roughly opposite to each other, but do not — obviously, 

 at least — alternate with the others. These two suckers 

 are opposite to each other and lie on the outside of the 

 scolex, and are about on a level with the hooked suckers 

 already described. It is quite possible that when the scolex 

 is fully expanded and not warped through unequal contrac- 

 tion with alcohol, the four suckers might alternate with more 

 regularity than is apparent in my preparations. In any case, 

 these suckers are quite different from those already described. 

 They are smaller than, at any rate, the larger of the more apically 

 placed suckers ; and there is no trace whatever of any hooks 

 associated with them. Each appears (see text-fig. 95) in section 

 to have the form of a flat disk. Their structure seems to be 

 quite like that of suckers generally among Tapeworms. What 

 is very apparent about these suckers is their very small size com- 

 pared with the wide periphery of the scolex. I could not detect 

 them at all on an examination of the scolex with a lens (see 

 text-fig. 93, p. 678). 



We have next to consider the histological structure of the 

 scolex, which presents certain peculiarities. The anterior region 

 of the scolex has no distinction into medullary and cortical layers. 

 The commencement of such a difllefentiation is marked by the 



45* 



