BY J. P. HILL. 



53 



extend through three thin sections, of which the middle one is 

 represented in Fig. 4. The cavity is lined by a d-^licate layer of 

 cuticle just as Mouticelli describes* for the terminal sucker of 

 Scolex polymorphus. The wall of the sucker he describes as 

 consisting of radial fibres similar to those of the suckers of Tre- 

 matodes. In the form under consideration, nuclei are readily 

 visible in the wall, but the cell boundaries could not be made out, 

 nor were the radial fibres distinguishable. 



In the tissue surrounding the sucker are numerous radially and 

 circularly running fibres. The radial fibres correspond to what 

 Monticelli callsf the retractor& of the terminal sucker. Like the 

 latter the radial fibres pass out from the central sucker and some 

 of them can be traced to the inner sides of the lateral suckers. 

 According to Monticelli, the retractors of the terminal sucker in 

 Scolex polymorphus are inserted into the dorsal side of the four 

 suckers. That the structure here termed the frontal sucker 

 represents the similarly named structure in Scolex polymorphus, 

 though in a somewhat reduced condition, is evident from the 

 foregoing. 



The morphological value of the frontal sucker of Scolex 2^oly- 

 morphus is considered at some length by Monticelli in the paper 

 already referred to.| He regards the frontal sucker and its 

 retractors as homologous with the frontal sucker and its muscula- 

 ture in Amphilina, and as homologous with the buccal sucker of 

 Treraatodes, as representing in fact the lost digestive tract of 

 Cestodes. 



1 quote his conclusions in full : — "In breve, saremno per tutti i 

 fatti esposti indotti ad ammettere una forma ancestrale primitiva 

 trematodiforme di Cestode fornita di bocca ed intestino, il quale, e 

 a poco a poco scomparso per effetto del parassitismo. E ad attestare 



* "Coutribuzioni alio studio della fauna elmintologica del Golfo di Napoli.' 

 Mitt. Zool. Stat. Neap. B. viii. 1888, p. 114. 

 t Loc. cit. p. 118. 

 + Loc. cit. pp. lis and 121. 



