FROM EGG TO INSECT^ — S'lQODORASS 



381 



chromosome pair, united in synapsis (fi*>;. 5 A, a), are again sepa- 

 rated on a division spindle and pass to opposite poles of the nucleus 

 to form the two new nuclei. After this division, therefore, each 

 new nucleus contains the same reduced number of chromosomes 

 as before (fig. 6 A, 6), but the chromosome material itself has 

 undergone a redistribution between the new nuclei, since the indi- 

 vidual chromosomes were not divided between them as in ordinary 

 cell division. The separated halves of the paired chromosomes do 

 not necessarily all go in the same direction, the male or female ele- 

 ment in some going to the one pole and in some going to the 



Fig. 0. — Maturation of an egg 

 A, diagram of chromosome division In maturation : each double chromosome 

 in nucleus (a), after synapsis (fig. 4C), divides into single chromosomes of nuclei 

 of first division (b) ; in second division, each single chromosome splits into two, 

 resulting in four nuclei (c), each with same number of chromosomes, but with 

 half the number contained in the original cell (flg. 4A). B, section of upper end 

 of egg of a honeybee just after maturation, showing the three small polar body 

 nuclei {PB), and the large functional egg nucleus {Nu) now ready for fertiliza- 

 tion. (Figure from Potrunkevitch.) 



other, so that whatever hereditary influences they may carry will 

 be distributed by chance in all possible combinations. The second 

 maturation division immediately follows the first, but in this di- 

 vision the original chromosomes divide lengthwise each into two 

 as in ordinary division, thus producing four nuclei, two of which 

 are replicas of one of the first-formed nuclei, and two of the other 

 (fig. 5 A, c). The chromosome number, however, is the same in 

 ail, the formula being 24-l<^ for nuclei descended from one with 

 six original chromosomes. 



Figure 5 A represents diagrammatically only what takes place in 

 the nucleus of the maturating egg cell; a truer picture of the results 

 of the maturation divisions is shown at B. Three of the new nuclei 



