BY J. P. HILL. 55 



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 tapeworms possessed a mouth 

 opening between the suckers," and further he regards " this pore 

 (frontal sucker), along with the muscular apparatus lying below it 

 (the rostellura or bulbus), as the morphological equivalent of that 

 sucker which is found between the lateral suckers, not only in 

 Riidol phi's Scolex and the associated Phyllobothria, but also in 

 some Tseniadje." 



Admitting then that the structure under consideration in T. 

 sag'inata is the homologue of the frontal sucker, found in a 

 more highly developed condition in other forms, and accepting 

 Leuckart's further observation, viz., that the rostellum in the 

 hook-beariug cystic worms passes through a developmental stage 

 similar to that which is retained as the permanent condition in 

 Tcenia sayinata, we have clear proof of the homology of the two 

 structures. The disappearance of the hook-fundaments which 

 surround the pore of the sucker in T. saginata is certainly due to 

 degeneration, but in the sucker itself we have clearly the persis- 

 tence in the adult of a developmental stage, early lost in the other 

 hook-bearing Tseniadse. These facts tend clearly to show that 

 phylogenetically the frontal sucker is the older of the two struc- 

 tures, and that as specialisation has proceeded it has been replaced 

 by the rostellum. 



If this be so, then we must regard the condition in Polycercus 

 Didymogastris, where, as we have shown,* the head, with the 

 rostellum, arises in the centre of a cellular mass, as an example 

 of the most highly specialised condition in the series. 



Excretory System.. — In the living Cysticercus examined under 

 compression, the longitudinal trunks of the excretory system were 



* "Oa Polycercus," P.L.S.N.S.W. (2), Vol. viii. p. 373. 



