TAPE-WORMS OF THE SUB-FAMILY AVITFLLININ.E. 343 



resemble, especially in silvered specimens. The reticulations 

 formed b}'^ the fibres enclose cavities which are probably in 

 connection with each other. This structure has only been 

 found in A vi tell in a; I have not observed anything" similar 

 in the other species I have examined. 



Within the homogeneous layer and separating it from the 

 subcuticular muscles lies an extremely thin membrane, the 

 basal membrane, which can usually be quite readily demon- 

 strated. The basal membrane is generally accepted as being 

 derived from the parenchyma. 



The formation of the cuticula has recently been studied by 

 Young (1908) in Cysticercus pisiformis; according to 

 him, " The cuticula of Cysticercus pisif ormi s is developed 

 from a groundwork of simple parench3'ma fibrillas by a 

 deposition among them of a cement substance. There are 

 no specialised fibrillae or cellular processes concerned in its 

 development. The fact that in its development the processes 

 of the subcuticular cells take part does not in any way 

 detract from the above statement, since primitively the sub- 

 cuticular cells themselves are undifferentiated parenchyma 

 cells." Further (p. 288), "The cuticula is formed before 

 the differentiation of the subcuticular cells." 



Young's opinions are totally opposed to Blochmann's (1896) 

 and his followers, who consider the cuticula to be mainly a 

 product of the subcuticular cells. 



It can, however, be proved from adult cestodes that the 

 cuticula is not derived from the subcuticula. There is no 

 doubt as to the presence of a cuticula consisting of comidial 

 and homogeneous layers on the surface of the suckers, yet 

 there are no subcuticular cells in the suckers. I have been 

 able to convince myself of their absence in Anoplocephala 

 magna (Abilgaard), Taenia serrata, Goeze, Dipylidium 

 caninum (L.), Stilesia hepatica Wolffhiigel. Young 

 (p. 225) also states, '^ The subcuticula cells are lacking in the 

 suckers." In all these species the cuticula above the suckers 

 is similar to that elsewhere, differing somewhat in this respect 

 from Avitellina centr ipunctata (Rivolta). There being 



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