METHOD OF CELL DIVISION IN MONIEZIA. 139 



Of the six cases here given, believed to be fairly representative, 

 in only one, Ai and A2, have the nuclei increased in greater 

 proportion than the volume, and even here the increase is only 

 slightly greater; in two, Di and D2, and Fi and F2, the two 

 ratios have kept pace with each other; while in four, Bi and B2, 

 Ci and C2, Di and D3, and El and 2, the nuclear ratio has 

 fallen more or less behind the volumetric. Now evidences of 

 division are no more and no less common in the parenchyma 

 cells than in the anlage so the result of these four cases favors 

 somewhat the notion of migration of the parenchyma nuclei to 

 the anlage for there are relatively fewer nuclei in the older pro- 

 glottids and it is hardly probable that degeneration, the opposing 

 factor, would play a part in the decrease in the number of nuclei 

 in as young proglottids as these are. But on the whole the evi- 

 'dence for migration is not strong; certainly this factor cannot 

 have been the important one in the formation of the anlage of 

 the female organs. 



It would seem, then, that here as is general throughout the 

 animal kingdom germ cells must arise by cell division. It is 

 the inconspicuousness of these processes that occasions the pres- 

 ent discussion. 



Mitosis unquestionably occurs. Child records and figures oc- 

 casional cases. Although he holds that they are too infrequent 

 to account for the cell proliferation he finds them in nearly every 

 stage of development. He has, however, never found them in 

 the early stage of the duct formation, in the primary anlage, 

 unless his recent account of a single individual consisting of 

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

 which nearly every nucleus is dividing mitotically may include 

 such cases. He has given no definite statement of the stages 

 included in this worm, but certainly the primary anlage appears 

 in the proglottids which are quite young. In these earliest 

 stages I have found a considerable number of mitoses although 

 they are by no means so abundant as to be seen upon a cursory 

 examination. Let me call attention to the fact that in almost 

 any tissue the ratio of resting to dividing cells will be found to be 

 very great. This ratio is a surprising one. 



In the oogenesis of Planorbis, a form in which divisions are 



