THE CELLULAR BASIS 133 



somes are homologous not merely in shape and 

 size but also in function, though this homology 

 does not amount to identity. 



In some instances it can be proved that one 

 member of each conjugating pair of chromo- 

 somes comes from one parent and the other 

 from the other parent, and it is probable that 

 this is always true. In every cell of every 

 individual which has developed from a ferti- 

 lized egg there are two full sets of chromo- 

 somes, one of which came from the sperm and 

 the other from the egg; but when this indi- 

 vidual in its turn produces germ cells homolo- 

 gous chromosomes of each set unite in pairs, 

 during the growth period. 



These sjmaptic pairs are the bivalent chrom- 

 osomes, and in addition to showing the line of 

 junction by which they are united they f re- 



paired. C, first maturation division after the 5 pairs of chrom- 

 osomes have pulled apart; the unpaired chromosome is going 

 entire to one pole of the spindle. D, two cells resulting from 

 this division, one containing 5 and the other 6 chromosomes. 

 E, four cells resulting from the division of two cells like D, in 

 which each chromosome has split into two so that two of 

 the cells contain 5 and two contain 6 chromosomes. F, two 

 of these ceUs changing into spermatozoa, one containing 5 and 

 the other 6 chromosomes. (After Mulsow.) 



