196 MR. F. E. BBDDARD ON A 



rostellum, renders it apparently absent or more feebly developed 

 in some individuals than in others. And there is here a resem- 

 blance to the otherwise not closely allied Taenia saginata. 



This median sucker is, indeed, a not much more developed 

 structure than the rudimentary rostellum of Tcenia saginata. In 

 this latter species Railliet* speaks of " le i-ostre faisant defaut et 

 se trouvant remplace frequemment par une legere depi-ession " ; 

 while Leuckart t, in defining the species, states that " the head has 

 a flattened crown with a pit-like hollow in the middle." On the 

 other hand, Kiichenmeister, while emphasizing the occasional 

 absence of any such depression in both text and figure, also 

 figures + an organ very like a sucker, and certainly moi'e than a 

 mere depression. The structure, however, is not, according to 

 Leuckart §, a sucker, but a rudimentary rostellum with a distinct 

 lenticular muscular mass. Leuckart's figure of a section through 

 this " sucker" is copied in Bronn's ' Thierreichs' (Bd. iv. p, 1203). 



The accompanying text-figure (text-fig. 20) shows a median 

 longitudinal section through the scolex of Otiditcenia, illustrating 

 the rudimentary rostellum and enabling it to be compared with 

 the adjacent suckers. The simplicity of the really sucker-like 

 rostellum will be apparent from this figure, which represents 

 the rostellum in a contracted state withdrawn into the scolex. 

 Inasmuch as the setse border the rostellum in a double circle, 

 they are not visible in such a preparation, only one or two being 

 seen in each section at the two corners of the rostellum. The 

 rostellum itself is obviously (to my mind) no more, or very little 

 more, developed than that of Tcenia saginata, already referred to ; 

 its muscular layer is not thicker than that of the suckers, as will 

 be seen from my figure. This obviously contrasts greatly with 

 complicated and more typical rostella ||. 



It will be observed, moreover, that the floor of the cavity into 

 which the rostellum is retractile — which floor constitutes the 

 rostellum — is hardly, if at all, thicker than the latei-al walls of the 

 cavity ; that the whole sti-uctvire, in fact, does not greatly differ 

 from a sucker. It may be borne in mind that this is a possible 

 origin of the rostellum, though the theory that it is the meta- 

 morphosed remains of a pharynx has been put forwai^d. On the 

 other hand, the nuclei are more densely packed in the rostellum 

 than in the suckers, as the figure referred to shows. This 

 difference is, however, perhaps partly due to the more contracted 

 condition of the rostellum, and possibly also to its greater con- 

 tractility. Again, the layer of chitin covering the rostellum is 

 very much thicker than that which lines the suckers — the latter 

 being, indeed, inappreciable. There is some black pigment in the 

 head behind the suckers. 



My preparations unfortunately do not allow me to give any 



* 'Traits de Zoologie Medicale et Agricole,' ed. 2, Paris 1895, p. 232. 



t • The Parasites of Man ' (Engl. ed. transl. by Hoyle), Edinburgh 1886, p. 407. 



X Loc. cit. pi. vi. tig. 8. 



§ Loc. cit. p. 435. 



II Of., e.g., Bronn's ' Thierreichs,' Bd. iv. figs. 56, 57, 58, pp. 1326-1328. 



