POLARITY AND BILATERALITV OF THE ANNELID EGG. 59 



2. An even more conclusive argument is afforded by cen- 

 trifuging ovocytes with intact germinal vesicle. As shown in the 

 paper already referred to, the large germinal vesicle passes to the 

 central pole ; it is the lightest constituent of the egg. If, there- 

 fore, the position of the nucleus determines polarity, the central 

 pole should become the animal pole in such cases ; the polar 

 bodies should form here. I made a number of experiments on 

 this subject in 1906 and 1908. The difficulties found in inter- 

 preting these experiments are : () that the stratification induced 

 by low centrifugal powers is relatively slight in the stage with 

 intact germinal vesicle, apparently owing to greater vicosity of 

 the ground substance at this stage, and (b) that it does not persist 

 to the time of formation of the polar bodies, owing to the process 

 of polarization of granules that follows the rupture of the germinal 

 vesicle, which I described in a previous paper. However, by 

 following individual eggs in which the position of the centrifuged 

 germinal vesicle is known, the relation of the polar bodies to the 

 position of the germinal vesicle can be readily ascertained. It is 

 then found that there is no fixity of relation whatever ; in other 

 words, the maturation spindle, which forms at the site of the 

 germinal vesicle, may migrate through the entire diameter of the 

 egg to become fixed at the opposite pole, or perform any lesser 

 migration. The same thing is demonstrated if the eggs are sub- 

 mitted to very high centrifugal powers ; under these circum- 

 stances the stratification persists up to maturation in some eggs 

 to a sufficient degree to demonstrate positively that the polar 

 bodies form in all positions with reference to the centrifuged posi- 

 tion of the germinal vesicle. 



Thus one cannot determine the place of formation of the polar 

 bodies by simply throwing the nucleus to the surface of the egg. 



A third argument may be based on comparative grounds. 

 Very many cases are known in which polarity determines the 

 position of the nucleus ; the literature on fertilization is full of 

 such cases. I know of no observations that tend to show deter- 

 mination of polarity by position of the nucleus. 



The results, then, certainly demonstrate that polarity is not a 

 result of the position of the nucleus or of any configuration of 

 granules. It follows that it is a property of the ground sub- 



