METHOD OF CELL DIVISION IN MONIEZIA. 159 



former suggestion that that structure might give a misleading 

 appearance of amitosis is not borne out. 



As polyspermy occurs here accessory sperm nuclei might be 

 wrongly interpreted as amitosis. The condition, however, is not 

 difficult to distinguish. 



Cell migration has already been discussed in detail as a method 

 of origin for the pre-oogonia. As stated before there is not much 

 evidence that it occurs. It certainly is not the exclusive factor 

 and probably not even an important one. 



There yet remains my suggestion that mitosis may be of short 

 duration and occur in waves or at more or less definite periods 

 depending upon some unknown physiological factor an inter- 

 petation which Child refuses to accept. He says ('10, p. 113): 

 " 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. 1 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 errors of observation, or something else than 

 nuclear division." Nevertheless, is not the position that "the 

 relative frequency of mitosis and amitosis in certain species and 

 even in single individuals may vary greatly according to con- 

 ditions" in its practical application an admission of my sugges- 

 tion? 



This suggestion is based first upon certain a priori consider- 

 ations. Beckwith described cleavage mitoses in Pennaria and 

 Clava occurring from 4 to 6 A.M. only; in certain insects and 

 many plants mitosis occurs at night only; in onion root-tips 

 there are two periods of mitotic activity daily, at I P.M. and at 

 II P.M. and if the specimens are collected at any other times 

 than these there will be found a paucity of division figures. I 

 have seen grass root-tips in which not a mitotic figure could be 

 seen although young cells of the proper age for multiplication 

 were abundant. Amitosis has never been suggested for such 

 cases as this. Secondly, the suggestion has support in certain 



*A young specimen, found subsequent to his earlier accounts, consisting of 

 scolex, neck region and a few of the youngest proglottids in which almost every 

 nucleus is undergoing mitosis. 



