314 R- T. YOUNG. 



hand into a flame cell, and on the other into a testis cell, cannot 

 of course be answered in the present state of our knowledge. 

 It is not unreasonable to suppose however that, as the result of 

 some slight initial difference, one might become more susceptible 

 to the presence of excreta in its environment and so develop into 

 a flame cell; while the other, less susceptible to such influence, 

 would follow its original course of development and become a 

 testis cell. 



There is in these cases evidently no continuity of development 

 of the various parts of the excretory system as contended by 

 Blochmann 1 and others, and discussed by me in an earlier 

 paper. 2 



Such facts further clearly argue against the Roux-Weismann 

 theory of mosaic inheritance, and in favor of Driesch's view that 

 developing cells are totipotent, so far at least as cestodes are 

 concerned. 



1 Blochmann, F., "Die Epithelfrage bei Cestoden und Trematoden," Hamburg, 

 1896. 



2 Young, R. T., "The Histogenesis of Cysticercus pisiformis," Zool. Jahrb., 

 XXVI., 183-254. 



