208 THE PERPETUATION OF ADAPTATIONS 



The Maturation Divisions. The maturation divisions in mall ' 

 and female organisms while similar so far as the chromatin 1 

 concerned do not result in the formation of the same numb/r 



MALE 



PRIMORDIAL GERM-CELLS 



DIPLOID NUMBER OF CHROMOSOMES 



(x-4 IN THIS DIAGRAM) 



MULTIPLICATION PERIOD 



MANY GENERATI 

 SPEffMATO 



PRIMARY 

 SPERMATOCYTE 



SECONDARY 

 SFERMATOCYTE5 



GROWTH PERIOD 

 5YNAPSIS 



UNION OF_CHROMOSOME5 IN PAIRS 

 ORMiNof (HKXPLOIO NUMBER) OF BIVALENTS 



BIVALENTS LONGITUDINALLY SPLIT 

 FIRST MATURATION DIVISION 



SPLIT CHROMOSOMES 



:OND MATURATION DIVISION 



SINGLE 

 CHROMOSQMIS 



PRIMARY OOCYTE 

 EGG) 



FERTILIZATION 



FIR3T CLEAVAGE 



FIG. 90. Diagram of the maturation divisions of the male and female germ 

 cells. Four chromosomes are present in all cells of the body of the case illus- 

 trated. (The polar bodies are represented as much larger than they actually are 

 in relation to the egg cell.) 



of mature germ cells. From each primordial egg cell only one 

 mature egg is formed while three rudimentary eggs called polar 

 bodies are formed which have no part in development but de- 

 generate and die. From each primordial cell of the spermato- 



