THE CHROMOSOMES 



81 



tries. The chromosomes come together in pairs (fig. 

 34^). Each maternal chromosome conjugates with a 

 paternal chromosome of the same kind. 



Then follow two rapid divisions (fig. 34, e-i) . At 

 one of the divisions the double chromosomes separate 

 (fig. 34, d-f) so that each resulting cell comes to con- 

 tain some maternal and some paternal chromosomes, 

 i.e., one or the other member of each pair. At the 

 other division each chromosome simply splits as in 

 ordinary cell division. In the male four sj)ermatozoa 



&' 





ia 



A)°tf 



■•■"s5J*.-N; ■- 









'•:~'5<^ 



•■^."Ji &■•:■■■.■■ 





Fig. 35. — Diagram illustrating the two maturation divisions of the 

 egg. In a the polar spindle is present at the periphery of the egg. The 

 three pairs of chromosomes (bivalents) are represented in black and 

 white; the white being the paternal and the black the maternal. In b 

 the conjugating chromosomes have separated and are moving to the 

 poles. In c the first polar body has been given off, leaving three single 

 chromosomes in the egg. In c these have split lengthwise and lie off the 

 equator of a new spindle. In e the daughter chromosomes have sepa- 

 rated and moved to opposite poles. In / the second polar body has 

 been given off and the first polar body has divided. Three single 

 chromosomes are left in the egg. 



