256 Edmund B. JVilson. 



lowing: "The differences between the quiescent trochoblasts and 

 the other cells does not necessarily signify that the former con- 

 tain a special substance which makes them distinctively trocho- 

 blasts from the time of their formation. Of course, at some time 

 they do become distinctly trochoblasts, but simply because of their 

 relation to the whole" (p. 664). I have cited this particular 

 case, since It Is precisely In the case of the trochoblasts that experi- 

 ment most Indubitably demonstrates self-differentiation Inde- 

 pendently of the position of the cell In the embryo. To 

 cite a more general statement, "The material separated 

 as the result of precocious segregation may, I believe, be 

 perfectly Indifferent material except as regards position" (p. 

 682). "Certain amounts, rather than certain kinds of material, 

 are stored up in certain cells just where they will be in position 

 to produce by coordinated action the 'desired result' " (p. 679. 

 Italics mine). I must own to some difficulty In grasping the con- 

 ception of a "precocious segregation of perfectly Indifferent ma- 

 terial"; but, this aside, it is clear that differentiation Is considered 

 to be effected, not through the specific and Inherent nature of the 

 substance of the individual cell, but through correlative action, 

 the hypothesis even being advanced that an important function 

 of the spiral type of cleavage Is to provide for this purpose the 

 most direct and intimate possible communication between the 

 blastomeres (p. 658, etc.). 



Llllle, who has contributed such valuable observations on the 

 progressive segregation and organization of the egg-substance, 

 and has recognized In the fullest degree the complexity of that 

 organization and the Importance of precocious segregation, never- 

 theless casts considerable doubt on the conception of prelocalized 

 germ areas ('01, p. 269), and feels constrained to take the po- 

 sition "That the entire organism in every stage of its develop- 

 ment exercises a formative influence on all its parts, appears to 

 me an absolutely necessary hypothesis" ('01, p. 273). I do not 

 doubt, as will appear beyond, that this position, with proper quali- 

 fication, is well grounded; but do not the phenomena of self-dif- 

 ferentiation, as shown in the Independence of grafts or in the 

 typical differentiation of Isolated blastomeres in Patella, show that 



