REDUCING DIVISION 311 



chromosomes is illustrated by Aa, Bb, Cc, Dd. A spindle 

 forms and the chromosomes that have previously united 

 in pairs separate without splitting and travel in opposite 

 directions. This is known as the reduction division, since 

 two cells are formed with only four chromosomes apiece 

 instead of eight. Each of these cells divides by the usual 

 process and the four that result undergo changes and 



J® , ,j(D. 



,rv''' '^-•^ Multiplication of early f^'' "'-Ytf^ 

 ,11? ®^ eera cells. "" @^ j® 



@' S) ^' @) ^@ 0' 'gj 



/ \ / \ /' \ '' \ / '*. / \ / \ / '• 



*"S«?!S^S4 h Pairing Of 4 ^^c^i! 



X >-< Cfcromosomos >r^ ^ 



\\ 

 / / \ \ 



<^ g) Redaction divi-QS-» a\^ 



Mgjhep 



/ \ I 



<?) ^ "? ? (jr ii 



i«tm-8 .ii i i ■■. i SORadUiBBtary gggs. 



1 1 1 "\ A 



nature Egg 

 \ rr^ortillzation of 



aarly j)evelopment 

 Fig. 75. — Diagram showing development o£ the germ cells. 



become mature sperm cells. Each mature sperm thus 

 has one half the usual number of chromosomes that char- 

 acterizes the cells of the body. The egg cells undergo a 

 similar reduction division, so that the union of a sperm 

 with an egg produces the specific number, that is, eight. 

 Were there no reduction in the germ cells a sperm uniting 

 with an egg would produce a cell with sixteen chromo- 

 somes, and it is known from experiment that the develop- 

 ment in such a case would be abnormal. 



Random Assortment of Chromosomes. — In the re- 

 duction division, as just described, the chromosomes are 



