POLARITY AND BILATERALITY OF THE ANNELID EGG. 



73 



it tends gradually to disappear as is to be expected, for it is ob- 

 vious that with a sufficient force the granules would be driven 

 through or out of areas of greater density very readily and would 

 segregate solely with reference to their specific gravity. With a 



FIG. 8. Diagrams to illustrate structure of the ground substance of the egg of 

 Cheetoptcrus as revealed by centrifuging. A and C, controls : the arrow in each repre- 

 sents the direction of the centrifugal force. B and D, resultant conditions after centri- 

 fuging ; B when the direction of the centrifugal force is as in A, D when the direc- 

 tion of the centrifugal force is as in C. i, spindle area ; 2, spongy area of control 

 e gg s > 2-2, secondary axis of centrifuged eggs ; j, dense ring-shaped zone in the 

 ground substance ; ^, relatively fluid zone ; J, ectoplasmic zone. The numbers have 

 about the same significance as in Fig. 4. b.c., basophile cap ; g.c., gray cap ; h.b., 

 hyaline band ; s.a. , spongy area of centrifuged eggs. 



speed of 7,500 revolutions in one minute at a radius of about 6 

 centimeters, one can hardly observe any trace of the concentric 

 arrangement (Fig. 9). Abundance of proof can be furnished for 



