OCCURRENCE OF AMITOSIS IN MONIEZIA. I 1 3 



ing in number. I have never, however, considered absence of 

 mitosis in such cases as proof of the occurrence of amitosis. Only 

 the actual observation of amitosis can prove that it is occurring. 



I wish to add to my earlier observations the fact that in a sin- 

 gle individual consisting of scolex, neck-region and a few of the 

 youngest proglottids, I have found almost every nucleus in mi- 

 totic division. This is the only case of the sort which I have 

 ever observed. Aside from this I have never seen a single case 

 of mitosis in this region of the body. I am inclined to beheve 

 that this is a young animal in the early stages of growth. In my 

 work on various other forms, as yet unpublished, I have found 

 considerable evidence in support of the view that amitosis becomes 

 more frequent as growth (with cell division) becomes more rapid. 

 In Planaria, for example, regeneration begins with mitosis, but 

 as the growth of the new tissue becomes more rapid amitosis 

 takes the place of mitosis. Patterson ^ has found that the fre- 

 quency of apparent amitosis increases in regions of rapid growth, 

 and other evidence to be presented elsewhere exists. 



For those to whom the positive observations on amitosis are 

 of little or no value as evidence this case of mitosis in the neck- 

 region of Moniezia opens a way for simple interpretation. They 

 will conclude, as Richards suggests (p. 320"), that mitosis is of 

 short duration and occurs in waves, i. e., is periodic, and that all 

 the other individuals observed by me are simply stages between 

 two such periods. At present, however, I cannot accept such 

 an interpretation as the correct one. Not only the cells of the 

 neck-region, but the cells of the scolex, which does not take part 

 in the growth of other regions are undergoing mitosis in this 

 specimen. Moreover, I am as yet unable to convince myself 

 that the many cases of apparent amitosis, which I have observed, 

 in the neck-region of other individuals, are all errors of observa- 

 tion, or something else than nuclear division. 



Concerning the structure of the nuclei in Moniezia, it may be 

 said merely that the non-chromatic portions of the " embryonic 

 nuclei" present widely different appearances with different fixing 

 agents. After Hermann's fluid the nuclear structure of the primi- 

 tive germ nuclei and the parenchyma nuclei is somewhat similar 



1 "Amitosis in tlie Pigeon's Egg," Anat. Am., XXXII., 5, 1908. 



