EAELY STAGES OP DEVELOPMENT OP THE RABBIT. 145 



There is only one other alternative that will account for the 

 apparent growth round of the inner mass on the inner wall 

 of the blastodermic vesicle, as far as I can see, and that is 

 actual active migration of the cells in question. Of course it 

 is difficult to bring evidence to show that they have not 

 migrated, since it is not possible, I fear, to follow the process 

 in any one and the same specimen. At the same time I cannot 

 find any evidence to prove that they have actually migrated. 



If a cell does migrate, like an Amoeba for instance, one 

 would expect to find evidence of protoplasmic protuberances or 

 pseudopodia. Of this I can find no trace. The majority 

 of the cells seem at first (figs. 38, 39) to be quite isolated 

 from each other, and to be approximately spherical, whether 

 examined in the perfectly fresh condition or after treat- 

 ment with various reagents. They are, it is true, slightly 

 flattened on the side by which they adhere to the vesicle wall 



Certain of the cells here and there are connected by threads 

 of protoplasm, but this, I think, is not a sign of pseudopodic 

 activity, but merely indicates the final stage in division between 

 the two cells. I have no doubt that these cells divide rapidly 

 after a time, though I do not think much activity of division 

 takes place during the first few hours after the apparent 

 migration begins. 



If one of these inner rounded cells is undergoing the process 

 of division, then, as the wall on which it rests expands, the two 

 dividing halves of the inner cell will be pulled apart, and a 

 strand of protoplasm connecting the two cells may remain for 

 some time. 



Of course it is just possible, I suppose, that these rounded 

 inner cells might migrate by means of a rolling motion con- 

 sequent on '^ streams'^ of protoplasm within them, as do some 

 protozoa. But is such a phenomenon known anywhere in the 

 metazoan body ? I cannot think we are justified in assuming 

 this without evidence, for when examined in the fresh con- 

 dition no such protoplasmic activity can I notice. 



When the cells are so isolated as I believe them to be during 



VOL. 37, PART 2. NEW SEE. K 



