208 



THE PERPETUATION OF ADAPTATIONS 



The Maturation Divisions. The maturation divisions in male 

 and female organisms while similar so far as the chromatin is 

 concerned do not result in the formation of the same number 



MALE 



PRIMORDIAL GERM-CELLS 



0_0_ V^WITH DIPLOID NUMBER OF CHROMOSOMES X 



'x-4 IN THIS DIAGRAM) 



MULTIPLICATION PERIOD 



' "T\ MANY GENERAT 

 . Vtt V'SPEWIATO 



GROWTH PERIOD 

 5YNAP5IS 



J UNION OP CHROMOSOMES IN PAIRS 



IHAPLOID NUMBER) OF BIVALENTS 



PRIMARY OOCYTE 

 (OVARIAN EGG) 



BIVALENTS LONGITUDINALLY SPLIT 

 FIRST MATURATION DIVISION 



I SPLIT CHROMOSOMES 



SECOND MATURATION DIVISION 



$ SINGLE 



CHROMOSOfltS 



FERTILIZATION 



SECONDARY OOCYTES 



EGG 1" POLAR BODY 



BODY 



ASE3) DIVIDES 



OVUM " V" POLAR BODY 



FIR.3T 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- 



