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is not the relatively rare and exceptional process which it has been 

 supposed to be. It seems not impossible, however, that the term 

 "amitosis" may be found to include a variety of nuclear phenomena 

 depending on quantitatively and perhaps qualitatively different con- 

 ditions and leading to different results. For example, in starving 

 planarians the terminal portions of the intestinal branches which are 

 about to undergo degeneration show polymorphic nuclei and frequent 

 amitoses but these differ in appearance from the amitoses in regener- 

 ating tissues, being much more conspicuous and of different type, 

 and undoubtedly lead to different results. Such degenerative amitoses 

 are often very conspicuous and this fact will probably account for the 

 hypothesis of Ziegler and Vom Rath, that all amitosis is degener- 

 ative and ends in death. Under experimental conditions various in- 

 vestigators have observed some forms of nuclear division which seem 

 to resemble amitosis and others which appear to be intermediate 

 between mitosis and amitosis. Whether these experimental cases are 

 of the same nature or due to conditions of the same kind as the 

 process of amitosis occurring in normal tissues cannot at present be 

 determined. 



I desire to call attention to one feature of the process as I have 

 observed it which appears to be of frequent occurrence. In many of 

 the figures (Fig. 1, III, VI, VIII; Fig. 2, IV, VII; Fig. 3, II, III, 



VII, XI; Fig. 5, V, X; Fig. 8, II, III, V, IX, XI; Fig. 9, I, IV, VI, 



VIII, IX; Fig. 12, I, II, VII, IX) the division appears to be taking 

 place inside the old nuclear membrane. I have observed many other 

 convincing cases of this kind in these and other species, especially in 

 Moniezia and Planaria and am forced to believe that they represent 

 division. 



Amitosis must be due essentially to the increasing physical or 

 physiological independence of different nuclear regions. If this is the 

 case the formation of a membrane about each region is the natural 

 consequence. It does not appear at all improbable that in some 

 cases the new nuclei may not occupy the whole area of the old 

 nucleus and that spaces remain between the old membrane and the 

 new. The old membrane, where it does not form a part of the boun- 

 dary of the new nuclei, gradually disappears and the two nuclei appear 

 as separate nuclei, often with flattened faces where they were pre- 

 viously in contact. In case the new nuclei occupy the whole area of 

 the old nucleus the process appears simply as a cleavage of the old 

 nucleus, but is not necessarily fundamentally different. It should per- 

 haps be said that great care has been taken to avoid optical delusion. 



