FORM AND SIGNIFICANCE OF THE EOSTELLUM. 



435 



Fig. 247.— Head of 

 Tcetiia saginata in longi- 

 tudinal section. ( x 25. ) 



in which the anterior processes of the hooks are embedded, this 

 coating is represented in T. saginata only by an annular diaphragm, 

 which lies as a lip on the outer wall of the 

 above-mentioned lenticular mass. This is more 

 or less markedly arched according to the curva- 

 ture of the latter, and has in its centre an 

 opening which is expanded below, and appears 

 sometimes rather deep, since the lenticular body 

 has not unfrequently a depression in its anterior 

 surface. This is the opening long since observed 

 by Bremser, and occasionally by other observers, 

 and the appearance of which has given rise to 

 the formerly prevalent idea that the tape-worms 

 possessed a mouth opening between the suckers. 



I have already noted (p. 351) that the peculiar 

 formation^ of this structure, as above described, 

 may also be observed at a certain stage in the 

 development of the hook-bearing cystic worms, 

 where it attains its final organization after the 

 hooks and their root-processes have been formed. 

 The state of affairs in T. saginata is therefore 

 far from interrupting the unity of type found in other forms. It 

 either represents in a permanent form the early phase, which has 

 remained undeveloped, or it is the result of retrogression. 



The resemblance is further increased by the fact that the border of 

 the diaphragm in T. saginata is also at first provided with a close circle 

 of little points, that is, with structures such as we saw to be the first 

 traces of the hooks. But the points do not develop, they retain their 

 primary form, and very soon disappear. Mtsche notes, however, that 

 occasionally some of these rudimentary structures persist round about 

 the central pore of the head.^ 



In the first edition of this work I regarded this pore, which I 

 called the " frontal sucker," along with the muscular apparatus lying 

 below it (the rostellum or "bulbus"), as the morphological equivalent 

 of that sucker which is found between the lateral suckers, not only 

 in Eudolphi's Scolex (p. 371) and the associated Phyilobothria, but 

 also in some Tseniadse. It must not be supposed from this that the 



' Unlike Kiiohenmeister, who finds this structure "sometimes but not always" in 

 Tania saginata ("Parasiten," 2d ed., p. 180), I have always found it when I looked for 

 it in the right way, and must therefore regard this rudimentary proboscis as a constant 

 character of this worm. 



'' Kuchenmeister's statement ("Parasiten," 2d ed., p. 180) that Heller has seen 

 twelve, sixteen, or even thirty-two short thick hooks on the head of Cysticercus bovia 

 is incorrect. Heller's observations (see p. 3ia) referredto many-hooked embryos. 



