Variation in Hooks of Dog-Tapeworms 5 



VI). The hooks are set into the tissues of the rostellum, each 

 hook resting in a sort of socket. The large hooks are located in 

 the inner row of the double crown, and project above the smaller 

 hooks which are in the outer row. Ktichenmeister did not con- 

 sider that the hooks possessed any movement other than that 

 occurring simultaneously with general motions of the rostellum. 

 According to his view there were no muscle fibers in connection 

 with the radical portion of the hook, therefore there could be no 

 special movement of the hook that would change its posture or 

 position in its socket. Examination of the preserved rostellum, 

 however, shows the presence of numerous muscle fibers, and ob- 

 servation of a number of the preserved heads shows the action 

 of the muscles, since in some cases the hooks are projected with 

 their, points directed toward the lateral border of the head, while 

 in other instances the hooks are retracted and the points directed 

 upward. Goeze (1782) speaks of having observed the live worm 

 protract and retract its hooks. The presence of two types of 

 hooks in the same head also may be taken as an argument for a 

 certain individual movement, which assists the parasite in bur- 

 rowing into the tissues of the alimentary canal. 



FUNCTION OF THE HOOKS 



Werner (1782), discussing the hooks of T. serrata, suggested 

 the idea that the hooks were sheaths for sucking bladders which 

 could be extruded and retracted, serving the purpose of securing 

 nourishment. This view was occasioned, of course, by an erro- 

 neous conception of the structure of the hook and of the true 

 character of the pulpy mass within the cavity of the hook. 



Goeze (1782) held somewhat the same opinion as Werner as 

 to the function of the hooks. Steinbuch (1801), however, con- 

 sidered the hooks to be organs of attachment, which, by tearing 

 the tissues of the intestine, also assisted the suckers in the work 

 of securing nourishment. 



Wagener (1854) describes the hooks of Cysticercus piriformis 

 as possessing a small opening at the point of the prong, and 

 thought that he had observed pulsations and movements within 



195 



