12 E. J. LUND 



that the details of part of this process were not observed. Figure 

 34 is a dorsal view while figure 35 is a ventral view: from this it 

 seems certain that the membranelles (ma) of figure 35 belong to 

 individual A while membranelles of individual B would be those 

 indicated by mb in figure 35. That this conclusion is correct 

 may be seen from figure 36, a ventral view drawn forty-nine 

 hours after isolation. In this ma is seen to be the original band 

 of membranelles belonging to individual A, while mb is the 

 remainder of the membranelles of B. Figures 37 and 38, drawn 

 at seventy-two and eighty hours respectively show that the last 

 traces of the membranelles of individual B were finally absorbed. 

 Only the large macronucleus remained to indicate that this now 

 apparently normal organism had once been made up of two nor- 

 mal individuals. The remarkable resistance of the differentiated 

 gullet of individual B to absorption when compared to the 

 ordinary process of digestion in this organism is noteworthy 

 (Lund '14). It seems that under certain conditions active dif- 

 ferentiated structures are relatively resistant to dedifferentiation. 



VI. DEDIFFERENTIATION IN OTHER ORGANISMS 



No attempt to review or abstract from the literature the facts 

 relating to dedifferentiation in metazoa will be made. This has 

 been done in an excellent summary and review by Schultz ('08). 

 Schultz formulated the observations on metazoa in terms of the 

 hypothesis that all phenomena of form regulation are somehow 

 related to and a result of the reversal of differentiation or de- 

 differentiation. In other words regeneration is a result of the 

 differentiation of dedifferentiated cells (See also Child, '15). 



Many facts derived from careful studies on tissues, organs and 

 whole organisms unmistakably point to this conclusion, and to 

 the conclusion that one type of differentiated cell may trans- 

 form into another type of cell having a different form and func- 

 tion. But as Schultz ('08) admits and as H. V. Wilson ('11) 

 states, to prove it would necessitate following one and the same 

 cell or its equivalent during the transformation. In the sponges, 

 where H. V. Wilson ('11) has shown that a dissociation of the cells 

 leads to partial or complete dedifferentiation with subsequent 



