274 



Cell as Basis oj Organic Activity 



some has split ; thus each synaptic pair consists of four half chromo- 

 somes. These groups of four are known as tetrads. Although there are 

 four units for a group, this must be considered a diploid condition. At 

 the metaphase of this first division, the two split members of each ho- 

 mologous pair are on opposite sides of the equatorial plate. At anaphase, 

 the homologous chromosomes separate with the split maternal chromo- 



SPERMATOGENESIS 



OOGENESIS 



PRIMORDIAL GERM CELL [2nJ. 



..FIRST MATURATION (REDUCTION) DIVISION. 



..SECOND MATURATION (EQUATION) DIVISION, 



SPERMATOZOAN 



Fig. 82. — Diagrams of spermatogenesis and oogenesis. Paternal 

 chromosomes, black; maternal ones, stippled. 



some of a pair moving to one pole and the split paternal chromosome 

 moving to the other. This first meitotic or maturation division is thus a 

 reductional division with the two resulting cells being haploid (N) in 

 their chromosome number. Each pair of homologous chromosomes be- 

 haves without reference to any other pairs ; thus the resulting cells will 

 have both maternal and paternal chromosomes. 



