METHOD OF CELL DIVISION IN MONIEZIA. 155 



there were 28 cleavage mitoses; in another of 211 embryos were 

 53 mitoses; in still another, 124 embryos showed 40 mitoses. 

 The evidence that these cleavages occur by mitosis is of the most 

 positive and convincing character. Cleavage mitoses are more 

 abundant in my material than the second maturation division 

 which is, of course, mitotic. 



Furthermore, I have seen only one condition which could 

 possibly be interpreted as amitosis; it is shown in Fig. 59. This 

 figure represents the stage following the telophase of the division 

 cutting off the third micromere. The same condition obtains 

 following other telophases, however. The nucleus after the 

 telophase at first takes on an irregular appearance but later 

 becomes rounded out into the typical shape. This stage is 

 exactly comparable to the reconstruction stage of the female 

 pronuculeus after maturation. It is to be interpreted as the 

 final phase of a mitosis rather than the precursor of an amitotic 

 division. 



In the later cleavages, although I have not as yet followed out 

 all of the cell lineage, I have never found any reason to doubt 

 that mitosis is the method of cell division. Mitosis certainly 

 occurs frequently and I have seen no evidence of amitosis. The 

 two figures given are of typical cases; further illustrations would 

 be mere reduplication of the evidence. 



In the smaller blastomeres I have never seen any sign of direct 

 division; on the other hand, Figs. 60 and 62 show cases of mitosis 

 in these cells. 



To the present writer the facts in the cleavage of Moniezia 

 seem to admit of no other interpretation than that mitosis is 

 the method by which segmentation is accomplished. 



SUMMARY OF THE EVIDENCE. 



This summary will include the evidence gained from the study 

 of the female sex products from the time of their appearance as 

 the primary anlage of the ovary to the completion of segmenta- 

 tion. It will not include the vitellarium of sex ducts since the 

 evidence given by them is not thought sufficient to be conclusive 

 in favor of either view. 



It has been stated that the cells composing the primary anlage 



