ORIGIN OF THE INDIVIDUAL 



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FIG. 125. Diagram of the general plan of spermatogenesis and oogenesis in animals. 

 The somatic, or diploid, number of chromosomes (duplex group) is assumed to be eight. 

 Male, to the left; female, to the right. A, primordial germ cells; B, spermatogonia and 

 oogonia, many of which arise during the period of multiplication; C, primary spermato- 

 cyte and oocyte, after the growth period, with chromosomes in synapsis; D, secondary 

 spermatocytes and oocytes, with haploid number (simplex group) of chromosomes, 

 which have arisen by the first maturation (reduction) division; E, spermatids (which 

 become transformed into sperm) and egg and three polar bodies which have arisen by 

 the second maturation (equation) division; F, union of sperm and egg (fertilization) 

 to form zygote with diploid number (duplex group) of chromosomes; G, chromosome 

 complex of cells after first division of the zygote, and of all subsequent somatic cells, 

 and germ cells until maturation. 



