STRUCTURE OF THE ROSTELLUM. 



401 



In summing up these peculiarities we have referred to the structure 

 of the rostellum. It consists, as we mentioned, of a lenticular bulb, 

 which bears hooks, and effects their movement by its variable con- 

 tractility. The projecting circular ridge of the rostellum is situated in 

 the interspace between the root-processes, and brings these into 

 contact with the adjacent surface in such a way that the longer so- 

 called posterior processes lie on the anterior surface. The latter only 

 requires to change its radius of curvature to be able to act by means 

 of the processes on the position of the hooks. This change of form 

 occurs all the more easily and readily, since not only is the musculature 

 of the bulb specially strong, but the subjacent body-muscles come into 

 special relation to the latter. 



Our knowledge of these arrangements is specially due to the in- 

 vestigations of Mtsche, 1 which were indeed primarily 

 concerned with Tcenia crassicollis, but which, according 

 to my observations, are also applicable to the other 

 tape-worms, at least to T. solium (of which Nitsche 

 was able to examine only one badly preserved specimen), 

 T. serrata, and T. cwnurus. Nitsche was, however, mis- 

 taken in regarding the bulb, which is the true rostellum, 

 as only an elastic cushion without proper contractility, 

 and only able to change its form and position by means 

 of the muscular apparatus which surrounds it as a shell. 

 The error involved in this conception is sufficiently 

 displayed when we compare Nitsche's " elastic cushion" 

 with the rostellum previously described in the case of 

 T. undulata, which only differs in this, that the bulb 

 and sac are much less muscular than in our cystic tape- 

 worms. To bring the structure of the latter into 

 harmony with the typical form, we only require to 

 suppose that the musculature has developed greatly 

 at the expense of the interior space, otherwise filled 

 with connective tissue, and has finally caused the cavity 

 to disappear. 



Not much more remains to be said regarding the his- 

 tological structure of the rostellum. Under a sharply gitudinal se 



T.CJ T i -i ft * O* * young T 



denned porous and structureless external coat one finds serrata, consisting 

 a great number of fine fibres, which have a very regular ^ of ( h ^ a g ^ nd 

 course, and which fill up the whole mass of the bulb, 

 with the exception of a few, mostly separated, connective-tissue cells. 

 The arrangement of the fibres reminds one in many particulars of 

 that previously described in regard to the sac-like rostellum of the 



1 Zeitschr.f. wiss. Zool. t Bd. xxxiii., p. 183 et seq., 1880. 

 20 



FIG. 234. Lon- 

 section 



cenia 



