68 



FRANK R. LILLIE. 



to have a thick and dense wall in which the spherules of the 

 spherular zone are especially aggregated. The intermediate 

 spongy zone appears wider. The striking similarity of this con- 



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FlG. 5. Section of an unfertilized egg of Chatopterus that stood in sea water two 

 hours and seven minutes before killing. 



figuration to that produced by low centrifugal powers will be 

 seen as the description proceeds. 



We may now compare the pictures presented by eggs of 

 this stage that have been centrifuged at different speeds : For 

 this purpose we shall select first an egg that was centrifuged 

 1,150 revolutions in 31 seconds at a radius of 13 centimeters 

 (Fig. 6). Comparison of a large number of eggs shows first that 

 the position of the eggs in the centrifuge is a matter of chance 

 and second that the segregation produced is essentially the same 

 in whatever direction the centrifugal force may act with reference 

 to the polar axis. We may therefore leave the question of direc- 

 tion of centrifugal force out of account. As already noted, the 

 effect on the living egg is very striking : it appears stratified in 

 the direction of action of the centrifugal force ; at the central 

 pole is a small gray cap, next to it a broad, clear or hyaline 



