EVOLUTION, HEREDITY, EUGENICS 



505 



tudinally split chromosomes meet {synapsis) in pairs, each of which 

 is composed of one maternal and one paternal chromosome. Thus 

 a quadruple chromosome {tetrad) is formed as in spermatogenesis. 



SPERMATOGENESIS 



OOGENESIS 



Primordial 

 Germ Cell 



Specmafo qonia 



Multiplication Period 

 (Diploid Number of 

 Dqad Chromosomes. 

 Mantj Generations) 



Growth Period 



(Si^napsis or Union of 



Like D II ads to Form 



Ha pi old Number of 



Tetrad Chromosomes 



No DiOisions) 



First Oocijte' 



Maturation Period 

 (Two DiOisions. First 

 Produces Dyad Chromosome^ 

 Second GiOes 

 Monad Chromosomes 

 Which Later 

 Split 

 Londltudinallu ) 



r\^ Transformation 



\yj\ Period 

 C^^^j (Applies to 

 ■-^^ t^ale Germ 

 Cells Onlij) 



Primordial 

 Germ Cell 



Ooqonia 



Second Oocyte 

 and First 

 Polar BodlJ 



t^ature Oi/um 



and 

 Polar Bodies 



Fertilization and Cleaoaae 



Fig. 260. Diagrams of spermatogenesis, oogenesis, and fertilization. Chromo- 

 somes derived from female are shown in solid color, those from male in outline. Sex- 

 chromosomes are shown with roughened contours. The diploid complex consists of a 

 double series, both as to size and shape, with the exception that the male has only one 

 sex chromosome. Note that it is always derived from his mother. (Courtesy of E. 

 Carothers, 1931). 



Subsequently, in the fi7-st maturation division, the tetrads divide 

 into dyads, then in the second maturation division they divide into 



