John P. Munson 317 



always the central cell. It differs from the follicle cells, so far as I can 

 see, in two important particulars, namely: First, its central position 

 gives it an environment of similar cells ; while the follicle cells have one 

 side adjacent to the egg, the other side adjacent to the surrounding 

 stroma cells. One would naturally expect that, if the differences in sur- 

 roundings could develop polarit}'', such should be found in the follicle 

 cells, while the egg should be homaxial. On the contrary, the oocyte 

 differs, secondly, from the follicle cells in having a centrosome at one 

 pole, which is evidently absent in, the follicle cells. 



Differentiation of the Oocyte. 



Seeing that the oocyte resulting from the division of the oogonia is 

 always the central cell, I have endeavored to ascertain the probable 

 cause of this. Is the egg a result of its accidental position amid its 

 sister-cells, and do the follicle cells simply become follicle cells because 

 of their accidental position with reference to the oocyte on the one hand 

 and the surrounding stroma cells on the other? In other words, is it a 

 matter of chance which of these cells shall become an egg, or is there 

 some internal difference in the cells, which results from a qualitative 

 division of the original oogonium? Eight here, it seems to me, lies the 

 problem of all problems, that of coll differentiation. The matter pre- 

 sents itself here in its simplest form ; for we have here evidently to do 

 with the first of those changes, ecdysis or moults through which the 

 original germ separates off from itself the somatic cells, which nourish 

 and protect it, and of which the development of the fertilized egg is 

 only a more complex process. May not this division of the oogonia be 

 compared to a simple process of cleavage, by which there results the 

 most primitive separation into germ and somatic cells? If intrinsic 

 differences arise in this group of cells from a qualitative division of 

 some sort, it ought to afford a strong presumption in favor of such a 

 process in the development of the fertilized egg; if, on the other hand, 

 the difference between the oocyte and the follicle cells is due to cellular 

 interaction, may this factor not be equally important in the later 

 ontogeny ? 



I have endeavored to discover the law according to which one of the 

 cells of this group comes to occupy a central position, but I cannot say 

 that I have been successful. There appears to be no regularity in the 

 direction of the spindles in the division of the four cells into eight, 

 which might determine the final position of the central cell. I am not 

 prepared to say, however, that no such law exists. Possibly the follow- 

 ing facts are sufficiently important, in this connection, to warrant a state- 

 ment of them. 



