2 78 LILLIE. [Vol. XVII. 



left to future investigation ; I have described here only what 

 seemed to me necessarily to follow from the phenomena accom- 

 panying the maturation, fertilization, and cleavage in Unio. It 

 is this orientation in the cytoplasm that gives a differential 

 value to mere position (Driesch), for "position" in an unor- 

 ganized mass of cytoplasm is unthinkable. We have sufficiently 

 considered the evidence for believing that this organization must 

 * be a property of the idiosomes ; and it seems to me at present 

 that Driesch's conception of bilaterality of these elements is 

 likely to prove a fruitful one. 



Vassar College, 

 May, 1900. 



