178 C M. CHILD. 



Doubtless, also, there are characteristic differences in different 

 species. In the life-history of Moniezia, for example, rapid and 

 enormous growth is a characteristic feature. In such a form 

 the stimulus to division and growth must be more powerful or 

 else the nuclei must react more readily than in other species in 

 which the life-history does not involve such extensive growth. 

 Whichever the case, we may expect to find the acyclical nuclear 

 phenomena more characteristic of the species with extensive or 

 indefinite growth than of others, simply because in the former 

 the amount of synthesis is much greater and relatively more 

 rapid than in the latter. If amitosis is associated with these ex- 

 treme assimilative conditions, as our hypothesis postulates, then 

 its distribution and frequency will follow the same rule. 



Similar differences may be expected in different organs and 

 regions of the individual, and so far as our knowledge goes at 

 present, they appear to exist. Amitosis seems to be more char- 

 acteristic of rapidly growing or assimilating organs and regions 

 than of other regions. 



If these observations and suggestions are correct, we can no 

 longer regard mitotic figures as the sole criterion of nuclear divi- 

 sion in organisms. In many forms, such, for example, as Pla- 

 naria, in mid-summer, when growth and nuclear division are 

 very rapid and fission is occurring every few days, mitoses are 

 rarely seen, but amitoses are very abundant. In various cases 

 of form-regulation, which were formerly supposed to occur with- 

 out cell-division because no mitoses were observed, amitosis is 

 very frequent. 



Furthermore, if amitosis may occur in the normal develop- 

 mental cycle and if it is especially characteristic of regions of 

 rapid growth, as the facts indicate, we cannot depend upon the 

 distribution of mitotic figures in developing tissues as an indica- 

 tion of the rapidity of cell-division and growth in different regions. 

 The regions where mitoses are most abundant may be the 

 regions of slowest division instead of the only regions where 

 division is occurring. 



The bearing of these and other observations on certain cyto- 

 logical hypotheses is briefly discussed in another paper (Child, 

 'oyc) and requires no further consideration here. I hope in 





