228 Egbert Thompson Young, 



Taking up now in their order the points enumerated above, the 

 first argument advanced in favor of the epithelium theory may be 

 dismissed with a few words. A union of sub-cuticiilar and paren- 

 chyma cells has been both claimed and denied. Blochmaxn (1896, 

 p. 6), himself the staunchest advocate of this theory, admits the 

 possibility of such a union when he says ■'. . . besonders wenn man 

 annimmt, was vorderhand noch nicht direct erwiesen ist, dass die 

 Ausläufer verschiedener Zellen anastomosiren, eventuell sogar mit 

 den die Nahrung von aussen aufnehmenden Epithelzellen in Ver- 

 bindung treten". In my own preparations I have demonstrated 

 beyond question the existence of such anastomoses both in the adult 

 and the larva (see Figs. 48 and 51). 



The assertion that the cuticula is the product of the sub- 

 cuticular cells and hence the latter must be epithelial because a 

 cuticula is deposited solely by such cells is a pure assumption not 

 based upon any observations. K. C. Schneider (1902), Leuckaet (1879 

 bis 1886) and others have pointed out the possibility of the cuticula 

 being a product of the basement membrane of the parenchyma. As 

 a matter of fact, the account of its development which I have given 

 shows that the cuticula is formed before the differen- 

 tiation of the sub-cuticular cells. It is a product of 

 the undifferentiated parenchyma wall of the body, 

 and therefore the future "neuro-muscular", parenchyma 

 and sub-cuticular cells all take part in its formation. 

 It is not an epithelial product. It is true that the peripheral 

 processes of the sub-cuticular cells do extend into and form part of 

 the adult cuticula, but it is not true that they alone enter 

 into its composition, since ordinary parenchyma fibres 

 likewise extend into and form part of it; and it is 

 primarily formed by processes of cells which have not 

 yet assumed the epithelial form and arrangement of 

 the adult sub-cuticula. 



The third argument advanced in favor of this theory I am not 

 prepared to discuss in detail, since I have not succeeded in diiferen- 

 tiating sense cells in Cysticercus pisiformis, much less in 

 tracing their development. Since, however, the larva originally 

 consists solely of undifferentiated parenchyma, the only conclusion 

 possible is that the original source of the sense cells, like that of 

 every other tissue, must be the parenchyma. Furthermore, the 

 argument that sense cells in other invertebrates are of epithelial 



