POLARITY AND BILATERALITY OF THE ANNELID 

 EGG. EXPERIMENTS WITH CENTRIFUGAL 



FORCE. 1 



FRANK R. LILLIE. 



In a previous paper (Lillie, '06) I attempted to show that the 

 direction of polarity of the egg of Chcstopterus is not modified by 

 any experimental redistribution of the visible elements, nucleus and 

 granules, and I therefore concluded that polarity is a property of 

 the ground substance of the protoplasm. In the present paper I 

 propose to examine the grounds for this statement, to attempt to 

 show that bilaterality comes in the same category, and to examine 

 the conceptions of polarity and organization that naturally result. 



I. POLARITY. 



Polarity manifests itself first in the egg of Chcstopterus when 

 the ovogonium becomes an ovocyte and takes its place in the 

 ovarian epithelium. It has then a free pole and an attached pole, 

 which have different physiological relations and exhibit different 

 morphogenic activities. When the egg becomes free from the 

 epithelium it is found that the original free pole becomes the 

 animal pole in development, and the attached pole becomes the 

 vegetative pole. The developmental processes take place with 

 reference to these poles ; thus the various granules of the egg 

 rearrange themselves in a definite polarized fashion, the polar 

 bodies have an absolutely determined relation to polarity, cleavage 

 takes place and the various organs arise in definite topographical 

 relations to the polarity. 



In the paper already referred to I showed that if the egg is 

 centrifuged with sufficient force the result is to separate the 

 protoplasm into three strata, viz.: a central grayish cap, an 

 intermediate hyaline or clear band which contains the nucleus 



1 The substance of a part of this paper was presented before the joint session of the 

 American Society of Zoologists, and Section F Zoology of the American Associa- 

 tion for the Advancement of Science, held in Chicago, December, 1907. (An abstract 

 was printed in Science, Vol. XXVIII., No. 702, pp. 905-907, June 12, 1908.) 



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