METHOD OF CELL DIVISION IN MONIEZIA. 125 



definitions are not sufficiently diagnostic to be of use in the work 

 here undertaken. 



For amitosis there is but one absolutely certain criterion, the 

 observation of living material and subsequent study of material 

 fixed under observation, and this is, of course, impossible in most 

 cases. In the absence of such a criterion only complete series 

 of all stages in the constriction and subsequent division of the 

 nucleus and attendant cytoplasm would seem sufficient warrant 

 for the assertion that amitosis is the prevailing form of division. 1 

 Even complete series are no assurance that part of the cells do 

 not divide mitotically or that mitosis does not occur periodically. 

 But given a complete series assumed or proven and taking no 

 account of periodicity, etc., the interpetation of doubtful cases 

 on the basis of the complete series follows logically. As will 

 appear later such a complete series is extremely difficult to estab- 

 lish in the cestodes; its assumption, therefore, in the face of the 

 above mentioned difficulties is ultra radical. The burden of 

 proof is upon the shoulders of him who makes the assumption. 



It is true, however, that a spirit of open-mindedness demands 

 an impartial consideration of uncertain cases, incomplete stages 

 and doubtful processes in the hope that an unprejudiced decision 

 may be reached. The refusal to consider such cases is as un- 

 scientific as is the drawing of sweeping generalizations from them. 

 In such a spirit of investigation I propose to set forth the facts 

 as I see them in the case of the anlage of the female sex organs 

 and its derivatives in Moniezia. I then wish to sum up the 

 evidence for and against the occurrence of amitosis in this form 

 and to consider various a priori suggestions which have been 

 made by investigators to cover this case. Finally, I wish to 

 make a comparison of these results with those of Tcenia upon 

 which I previously worked. In the development of the anlage of 

 the female sex organs the history of the sex cells themselves, of 

 the vitellarium and of the ducts and canals will be considered. 



Interesting in this connection are the recent comments upon 

 Child's position made by Boveri. 2 



l To forestall criticism of this point, let me say that this is in no sense a precon- 

 ceived hypothesis. I had worked on the amitosis question nearly two years before 

 the significance of this contention was fully borne in on me. It is given thus early 

 in the discussion merely to make the account more intelligible. 



2 "Zellenstudien," 6, p. 235. 



