204 



REDUCTION OF THE CHROMOSOMES 



the eighty-four dyads give rise to a reticular cleavage-nucleus. From 

 this arise eighty-four thread-like chromosomes, and the same number 

 appears in later cleavage-stages. 



(b) It is the second and rarer mode that realizes Boveri's concep- 

 tion (Fig. 101). Both polar bodies are formed, the first removing 

 eighty-four dyads and leaving the same number in the egg. In the 



D 



E 



Fig. 101. Second type of maturation in the parthenogenetic egg of Artemia. [BRAUER.] 

 A. Formation of second polar body. D. Return of the second polar nucleus (p. 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. E. First cleavage-figure with 

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



formation of the second, the eighty-four dyads are halved to form 

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

 Both these groups remain in tJic egg, and each gives rise to a sttig/e 

 reticular nucleus, as described by Boveri in Ascaris. These two nuclei 

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

 to eigJity-four chromosomes, precisely like two germ-nuclei in ordinary 

 fertilization. The one hundred and sixty-eight chromosomes split 



