I 12 C. M. CHILD. 



from a"]?single neck-region and observe that the number of 

 nuclei in theTneck-region at any given time is sufficient 

 for only a few proglottids it becomes evident that during the life 

 of the animal an enormous number of new nuclei is formed in 

 some way in this^region. These facts dispose of Richards' con- 

 clusion that the parenchyma grows chiefly by the formation of 

 " intercellular material." 



Moreover, in view of these facts it is not in the least surprising 

 that Richards has failed to observe any division, either mitotic or 

 amitotic in the parenchymal cells (p. 323), since, so far as can be 

 determined from his statements, he has apparently paid little or 

 no attention to]the]neck-region. Mere observation of the method 

 of growth and the abundance of nuclei in this region forces us to 

 conclude, either that nuclear divisions occur in enormous 

 numbers in this region or else that nuclei are formed de novo, an 

 alternative which most of us would hesitate to accept without 

 proof of the most conclusive character. 



When one examines scores of these neck-regions, as I have 

 done, and finds first absolutely no mitoses and second hundreds 

 of cases of apparent amitosis, many of them almost diagrammatic, 

 the evidence for^the occurrence of amitosis acquires at least some 

 value. 



On p. 322 Richards says : " Child has assumed all through 

 his work that the absence of mitotic figures in tissues known to 

 be growing rapidly is evidence of the occurrence of division by 

 amitosis." He then proceeds to show that the growth of the 

 parenchyma occurs to a large extent by the formation of " inter- 

 cellular material." This statement of Richards seems, so far 

 as it concerns my own position, to be an error. My argument 

 is actually as follows : When mitosis is absent from regions where 

 rapid increase in the number of nuclei is manifestly taking place, 

 we have good reason to believe that some other form of nuclear 

 division is occurring, especially when we have discovered what 

 appears to be this other form in other tissues of the same animal. 



I have, I think, made it sufficiently clear all through my work 

 that in speaking of regions of rapid growth I meant not merely 

 regions in which the cells were increasing in size or forming in- 

 tercellular material, but those in which they were actually increas- 



