ON THE NUMBER OE POLAR BODIES, 



ETC. 



CONTENTS. 



PAGE 



Parthenogenetic and Sexual Egg o^o 



The process of the formation of polar bodies very widely 



distributed ......... 



The significance of polar bodies according to Minot, Balfour, 



and van Beneden ........ 



My hypothesis of the removal of the histogenetic part of the 



nucleus ....... 



349 

 350 



35' 



Confirmation by the discovery of polar bodies in partheno- 

 genetic eggs 355 



Parthenogenetic eggs form only one polar body, while eggs 



requiring fertilization form two ..... 356 



Parthenogenesis depends upon the fact that the part of the 

 nucleus which is expelled from sexual eggs in the 

 second polar body remains in the e^g .... 358 



History of this discovery ....... 359 



II. Significance of the second Polar Body .... 363 



Refutation of Minot's theory ...... 364 



The second division of the nuclear spindle invoK'es a reduc- 

 tion of the ancestral germ-plasms ..... 366 



The theoretical necessity for such reduction . . . 367 



Phyletic origin of the germ-plasms in existing species . . 368 

 The necessary reduction takes place by a special form of 



nuclear division ........ 369 



The division which causes this reduction has probably been 



already observed . , . . . . . -371 



Van Beneden's and Carnoy's observations . . . -37' 



Two different physiological effects of karyokinesis . . 375 



Significance of direct nuclear division ..... 377 



Arguments in support of the view that the division of the 

 egg-nucleus which causes reduction must occur at the 



end of ovogenetic development ..... 378 



Such nuclear division is to be found in the formation of the 



second polar body ........ 379 



History of the origin of this view ...... 380 



