TAPE-WORMS OF THE SlB-FAMIfA' AVITELLUs'INJ:. 347 



ployed by Zernecke is probably not quite satisfactory, apart 

 from its capriciousness and unreliability. 



In older proglottids the subcuticular cells atrophy, their 

 nuclei becoming smaller, their nucleolus and chromatin form- 

 ing apparently a single mass filling the entire nucleus ; and 

 the outlines of the cells themselves become indistinct (fig. 21). 



Havingr shown that the subcuticula belonos to the dorso- 

 ventral and transverse muscle systems, and that the cuticula 

 of the suckers arises independently of a subcuticula, and 

 bearing in mind Young's observation of the development of 

 the cuticula in Cysticercus prior to the differentiation of 

 the subcuticular cells, it will be seen that serious doubts must 

 again arise concerning the epithelial nature of the subcuticula. 

 Balss (1908) also opposes the theory that the subcuticula is 

 an ectodermal epithelium ; he considers both cuticula and sub- 

 cuticula to be of mesodermal origin, but he still admits that 

 the cuticula is a product of the subcuticula. Of course the 

 mere fact that the subcuticular cells form part of the dorso- 

 ventral and transverse muscles would not induce me to deny 

 their epithelial nature and their being the producers of the 

 cuticula ; remembering the epithelial muscles of hydroids, etc., 

 it is mainly on account of the cuticula being formed in places 

 where there is no subcuticula. 



The Musclks. Figs. 22-29. 



The muscles in the strobila, scolex, and suckers can every- 

 where be divided into the two groups, subcuticular muscles 

 and parenchj'uia muscles. 



The subcuticular muscles form two layers, whose fibres 

 run at right angles to each other ; the outer of these is 

 situated very close to the cuticula, and runs horizoutall}', the 

 inner runs longitudinally. 



The pai'euchyma muscles in the strobila form three distinct 

 muscle systems — the dorso-veutral, the transverse, and the 

 longitudinal muscle systems. The first two are much 

 weaker than the last. 



