556 



Before concludiug this description it should be stated that three 

 isolated cases of mitosis have been found in the parenchyma, two of 

 them lateral to the longitudinal nephridial canals where they could 

 not be connected with the development of either testis or ovary since 

 neither occurs in this region, and one near the developing ducts. These 

 divisions were found at a stage when mitoses were appearing occasionally 

 in the testes, but the ovaries had not yet developed. 



General Considerations. 



That amitosis is a very common method of cell division is indi- 

 cated by the frequency with which its occurrence has been noted in 

 the most various forms and tissues during the last few years. The 

 current belief that mitosis is the usual and more important method of 

 cell-division is doubtless responsible in many cases for the failure to 

 observe the occurrence of amitosis. Undoubtedly mitosis is much more 

 easily distinguishable than amitosis and in cases where a few mitoses 

 are visible the observer is likely to conclude without further search 

 that mitosis is the characteristic method of division. In the paren- 

 chyma of Planaria, where I have found occasional cases of very distinct 

 mitosis and in various rapidly growing embryonic tissues amitosis is 

 certainly much more frequent than mitosis. I believe that in many 

 cases careful study will show that the mitoses occurring in rapidly 

 growing tissue are wholly inadequate to account for the rapid increase 

 in the number of nuclei. These points will be discussed more fully 

 elsewhere. 



It is scarcely possible that Moniezia differs from the majority of 

 other forms in the amitotic multiplication of its sexual nuclei. Future 

 investigation will probably show that amitosis is at least as important 

 in the life of the cell as mitosis. 



If my observations are correct it is necessary to revise some current 

 hypotheses regarding the significance of mitosis and the relations be- 

 tween mitosis and amitosis. At present I desire to offer only a few 

 suggestions upon this point, which, however, are not entirely new. 



It is evident that intense nuclear activity accompanies the growth 

 of the cestode proglottid. The enormous development of non-nuclear 

 substances in the parenchyma as well as the rapid nuclear division in 

 earlier stages of development are indications of this. Examination of 

 the developing organs gives the impression that the greater the nuclear 

 activity the more frequent the amitosis. In the ovaries and testes it 

 is only in later stages as the rapidity of nuclear multiplication apparently 

 decreases that mitosis becomes frequent. The suggestion has been 



