io6 



FRANK R. LILLIE. 



the result that the inner dense zone presses in one or another 

 direction on the spindle and displaces its inner end. In other 

 cases the spindle is moved some distance from the surface into 

 the hyaline band ; this result is more commonly found with the 

 higher centrifugal powers. 



The normal relation of the spindle to the zones of the ground 

 substance is illustrated in Figs. 3, A, and 4, A. The inner end of 

 the spindle reaches to the inner dense zone and its antipolar rays 

 are embedded in the latter, which is indented by the spindle. If 

 now the centrifugal force acts parallel to the axis of the egg with 

 the animal pole in a central position, the egg elongates in this 

 axis. If the outer end of the spindle remains attached to the sur- 

 face, the inner end tends to be withdrawn from the inner dense 

 zone, and the basophile cap formed lies outside of the area of 



FIG. 3. A, diagram of zones of the ground substance in the normal egg and the 

 relations of the spindle. B, diagram to illustrate the effect of centrifugal force on the 

 ground substance and spindle acting in the direction of the arrow. I, karyokinetic 

 figure ; 2, central spongy area of control egg ; 2-2, direction of action of centrifugal 

 force ; 3, inner dense zone ; 4, outer more fluid zone ; 5, ectoplasmic zone. The 

 numbers "have essentially the same significance as in Fig. I ; b.c., basophile cap ; g.c. , 

 gray cap; h.b. , hyaline band. 



the spindle. If, however, the inner end remains fixed, the outer 

 end is withdrawn from the surface, and the inner end is embedded 

 in the basophile cap. 



If the centrifugal force acts at right angles to the axis of the 

 egg, the inner end of the spindle tends to be swung in a proximal 

 direction, (Figs. 3, A and B} both because the specific gravity of 

 the spindle as a whole carries it in that direction, and also because 

 the contraction of the egg in its own axis brings the dense zone 



