THE BIOLOGY OF THE CELL SURFACE 



currents which move the inclusions. This movement is 

 most striking in eggs with determinate cleavage — especially 

 if the inclusions be colored and hence easy to identify. 

 They come to lie constantly in definite regions of the egg 

 at first cleavage. If these fixed positions of the inclusions 

 be responsible for differentiation, then altering them should 

 modify or hinder development. 



By centrifugal force the normal positions of the cytoplas- 

 mic inclusions can be altered. The materials, which as 

 spherules and granules are suspended in the cytoplasm 

 normally without reference to their specific gravity, are 

 when the eggs are centrifuged moved to new positions and 

 stratified according to their respective specific gravity. 

 Thus oil, yolk and pigment form layers in the order named 

 with a zone of clear cytoplasm beneath the oil. Here our 

 interest focuses on two results obtained from the centri- 

 fuging of eggs.i 



The first deals with the fact that centrifugal force in 

 altering the position of the inclusions does not alter the 

 direction of the cleavage planes. Hence, the new arrange- 

 ment of the inclusions induced by centrifugal force, which 

 shifts them to blastomeres in which in normal development 

 they would not come to lie, has no effect on the develop- 

 ment of the embryo. It should be emphasized that this 

 effect of centrifugal force is the same in eggs with deter- 

 minate and indeterminate cleavage. Investigators are 

 agreed that the altering of the position of the cytoplasmic 

 inclusions has no effect on embryo-formation: the eggs 

 develop normally although the inclusions come to lie in 



^ Although centrifuging may be a violent method of treating eggs, 

 capable of causing their destruction, it can, if used with discretion, 

 leave them quite uninjured. One can soon learn the least amount 

 of centrifugal force necessary to stratify the cytoplasmic materials; 

 there is here no point in using a greater, as Conkhn did on the 

 ascidian egg. 



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