POLARITY AND BILATERALITY OF THE ANNELID EGG. 



55 



or spindle, and a distal yellow hemisphere which contains the 

 larger granules known as yolk (Fig. i). The results prove that 

 the eggs are not oriented in the centrifuge with reference to the 

 original polarity, and therefore the axis of stratification bears all 



FIG. i. Diagram of a centrifuged egg of Ch^topterus. a. p., animal pole; c.p. , 

 central pole, or pole turned towards the axis of the centrifuge ; d.p., distal pole, or 

 pole turned away from the axis of the centrifuge ; g.c., gray cap; H.B., hyaline or 

 clear band ; .r., maturation spindle; v.p., vegetative pole ; Y.ff., yellow, yolk -bear- 

 ing, or distal hemisphere ; /-/, primary axis ; 2-2, secondary axis. 



possible relations to the polar axis of the egg. We may call the 

 original polar axis the primary axis, and the line through the 

 center of the egg in the direction of the centrifugal force the 

 secondary axis (Fig. i). 



If such eggs are fertilized the polar globules of different eggs 

 form at any point of the surface with reference to the secondary 

 axis. Cleavage takes place with reference to the axis defined 

 by the polar globules, as in the normal egg, and is approxi- 

 mately normal in form. It therefore follows that the distribution 

 of yolk and other substances induced by the centrifuge is sub- 

 stantially immaterial so far as the form of cleavage is concerned. 

 The effect of abnormal distribution of yolk and other substances 

 on the differentiation of organs is not considered here. 



On the basis of these results I concluded that the polarity of 

 the ovum had not been affected by centrifuging, and that the 



