METHOD OF CELL DIVISION IN MONIEZIA. 137 



ment takes place somewhat more slowly than that of the inward 

 proliferation of cells, due, doubtless, to the fact that its function 

 is exercised only relatively late. 



The inward "proliferating area gradually extends somewhat 

 toward the median plane and somewhat toward one surface of 

 the proglottid known as the ventral surface. ... As the inner 

 and ventral end of the proliferating area approaches the inner 

 layer of circular muscles it spreads out into a flattened somewhat 

 disc-like area exactly as if it had encountered resistance to its 

 growth in the original direction and so had begun to spread out 

 in other directions." 1 A little later the posterior portion of the 

 anlage of the ovary becomes the anlage of the vitellarium which 

 develops about the middle part of the oviduct. This origin 

 shows that morphologically the vitellarium is part of the ovary 

 and gives credence to the view expressed for similar cells of other 

 animals (test cells of ascidians, etc.), that the cells are rudi- 

 mentary eggs. 



There are two regions concerning whose method of growth it is 

 especially important to have definite knowledge. These are the 

 primary anlage and the early embryos. Concerning the former 

 there are four possibilities as to the growth of the cells: origin 

 de novo, by migration from the surrounding parenchyma, and 

 by cell division direct and indirect. The first of these as Child 

 remarks ('10, p. 112) is "an alternative which most of us would 

 hesitate to accept without proof of the most conclusive char- 

 acter." 



Migration of nuclei to this region, if one could show that it 

 occurred, would explain the relative lack of mitoses in the an- 

 lagen. It would then be necessary, of course, to seek for mitoses 

 or amitoses in the neck region to determine the method of origin 

 of the cells. But actual evidence of migration is as impossible 

 to obtain as is evidence of amitosis. At best only indirect evi- 

 dence of it can be secured. 



If abundant divisions occurred there would be little probability 

 of migration, although it might occur. Abundant divisions are 

 not to be seen, however. On the other hand, the fact that many 

 of the nuclei in the primary anlage are smaller than the paren- 



1 Child, '076, p. 99. 



