242 O. C. GLASER. 



per cent, of mitosis, and 3 per cent, of amitoses. Allowing for 

 errors, there is practically no fluctuation in the frequency of either 

 mitotic or amitotic division in these three stages of development. 

 Since this is true, to say that the rate might have been very dif- 

 ferent between stages III. and IV., and again between stages IV. 

 and V., may be true, but is supportable by neither facts, nor 

 probability. Indeed, it is not going too far to say that the per- 

 centages as well as the number of cells found, indicate the exact 

 opposite, namely : that in this tissue, at this particular period of 

 development, mitosis and amitosis occur at constant frequencies. 

 Considering the table as a whole, it follows that of 3,340 

 nuclei, a little less than .6 per cent, exhibited mitotic figures. 

 If my interpretation of what constitutes amitosis is correct, then 

 a little over 87 per cent, of all divisions are direct, whereas only 

 a trifle more than 12 per cent, are mitotic. As I have pointed 

 out before, these figures undoubtedly contain a large error due 

 to the fact that early as well as late stages in amitosis are not 

 sufficiently well marked to enable one' to decide whether they 

 belong into this category or into that of the resting nuclei. As 

 all doubtful cases were relegated to the latter group, I feel confi- 

 dent that 87 per cent, represents the minimum of amitosis, and 

 that in all probability the direct divisions are more frequent. In 

 view of this I think that the conclusion is justified that amitosis 

 is the chief mode in which the nuclei and cells increase in number. 

 Of the two alternatives which these results allow, one, the possi- 

 bility of epidemics of mitosis, is not only unfounded, but improb- 

 able ; the other, namely, that a four-fold increase in cells can be 

 accounted for on the basis of 1 mitosis in 1,751 nuclei, involves 

 an absurdity. 



Discussion. 



I do not propose to enter at this time into an elaborate discus- 

 sion of either the literature on amitosis, or of the theoretical 

 questions on which direct nuclear divisions are thought to bear. 

 The former has been very ably done by other writers, notably 

 Henneguy ('96) and Wilson ('02), the latter I shall do after I 

 have accumulated more data. The belief that in the entoderm 

 of Fasciolaria we have an instance in which amitosis plays an 

 important if not the chief part in the differentiation of a definitive 



