TAPEWORM PROM APTERYX. &3 



erection of the acanthophore (see the series of figures, 16 

 — 18). The first movement is effected by the contraction 

 of the walls of the receptaculura rostelli. The fluid contents 

 are merely compressed, and force the rostellum forwards, 

 the acanthophore being thus protruded from the receptaculum 

 (fig. 17), and ultimately through the aperture at the true apex 

 of the scolex (fig. 18). 



The distension of the acanthophore is effected by the con- 

 traction of the wall of the rostellar sac, the reservoir. This 

 drives the fluid contents {t.) forwards, distending the acan- 

 thophore and pushing forwards the membrane, so that a 

 more or less spherical ball is formed, the wall of which is 

 tensely stretched (figs. 19, 20). The radial muscles now 

 come into action. Hitherto, as the various figures show, 

 they have been horizontal, but as the membrane to which 

 they are inserted is pushed outwards they take on the vertical 

 position, and are considerably stretched. 



During this process of protrusion the points of the hooks 

 ai'e kept pressed down against the side of the acanthophore, 

 but now by the contraction of the radial muscles it appears 

 that the terminal membrane, and therefore the " guard," is 

 pulled downwards, and consequently the point is caused to 

 diverge. 



This type of rostellum — with two concentric muscular sacs 

 — has been described by Leuckart, von Linstow, and others 

 for certain species, e.g. '^ Taenia " undulata, T. puncta, 

 T. serpentulus, — all avian Cestodes ; and it differs from 

 the apparatus in mammalian Cestodes, e. g. T. crassicollis, 

 which is a solid mass of muscles, having various directions. 

 I believe, however, that I have been able to add some details 

 in regard to it and to clear up some points that were doubtful, 

 and I have thought it worth while to give the series of 

 figures representing accurately the relations of the various 

 parts during its movement, as I know of no such series having 

 been hitherto published. 



DUNEDIN ; May 11 th, 1899. 



