MATURATION OF PARTIIENOGENETIC EGGS 



28 



two daughter-groups, each containing eighty-four single chromosomes. 

 Both these groups reviain in the egg, and eaeh gives rise to a singli 

 i^eticular ujccleiis, as described by Boveri in Ascaris. These tzvo niiclei 

 place themselves side by side in the cleavage-figure, and give rise each 

 to eighty-four cJironiosomes, precisely like two germ-nuclei in ordinary 

 fertilization. The one hundred and sixty-eight chromosomes split 













A 





B 



D E 



Fig. 142. — Second type of maturation in the parthenogenetic egg of Arh-mia. [BraL'ER.] 

 A. Formation of second polar body. D. Return of the second polar nucleus ( />. b?) into the 

 egg; development of the egg-amphiaster. C. Union of the egg-nucleus (?) with the second 

 polar nucleus {p. b?-). D. Cleavage-nucleus and amphiaster. /:". First .l.Mvage-figure wiili 

 equatorial plate containing 168 chromosomes in two groups of 84 each. 



lengthwise, and are distributed in the usual manner, and reappear 

 in the same number in later stages. In other words, the second polar 

 body here plays the part of a sperm-nucleus precisely as maintained 



by Boveri. 



In all individuals arising from eggs of the first type, therefore, the 

 somatic number of chromosomes is eighty-four; in all those arising 

 from eggs of the second type, it is one hundred and sixty-eight. This 



