METHOD OF CELL DIVISION IN MONIEZIA. 157 



preted as favoring the amitosis view: the condition represented 

 in Fig. 59. 



The evidence opposed to amitosis and favoring the view that 

 mitosis is the method by which divisions occur is as follows: 



First, mitotic figures do occur throughout all stages of the 

 development of the tissues considered, and they occur in the 

 peripheral (or growing) regions of the organs. Analogy may be 

 drawn from cases like Planorbis and Ascaris in which the oogonial 

 divisions are very difficult to find, and yet are known to occur 

 regularly. 



Second, stages of nuclear constriction are not found in suf- 

 ficient number to account for the arrangement of the nuclei in 

 pairs if amitosis be the method by which they arise. It is logical 

 to expect that steps in the process would be found if the arrange- 

 ment in pairs is the end result of amitotic division. As has 

 been repeatedly stated, it is not possible to establish a complete 

 series of stages in the auto-constriction of nucleus and cell body. 

 If periodicity is a factor in cell division (see below) the arrange- 

 ment may be looked upon as favoring the mitosis view. Finally, 

 it is most probable, although impossible to prove, for the pre- 

 oogonia and oogonia are not favorable for such study, that there 

 may be some movements of the halves toward each other anal- 

 ogous to the movements of telekinesis in other tissues, for in all 

 cases carefully studied with regard to this point, including de- 

 veloping eggs, epithelial tissues, etc., such movements have been 

 found. I have myself found evidences of them (not shown in the 

 present series of figures) in the cleavage of Moniezia. 



Third, the occasional cases of constriction and indentation 

 which occur have not been shown to be normal steps in division. 



Fourth, the condition represented in Fig. 59 is, as previously 

 stated, the final stage of mitotic division rather than the be- 

 ginning of amitosis. 



Fifth, the evidence favors periodicity as a factor in mitotic 

 divisions. (See below, under discussion.) 



Sixth, that the maturation and first cleavage alone should 

 occur by mitosis as described by Child is difficult to reconcile 

 with amitotic divisions elsewhere throughout the series. 



Seventh, the evidence that the cleavage divisions occur by 



