THE GREAT RELAY RACE 467 



egg on its developmental way. An opposing school of "spermists" 

 maintained that the egg was only useful as a means of food storage 

 for the essential sperm. Notwithstanding the fact that the ancient 

 Assyrians were well aware that date palms would not mature fruit 

 unless pollen from male trees was dusted on the blossoms of the 

 female trees, it was less than a century ago that it was finally estab- 

 lished by Leuckhart (1822-1898) that both egg and sperm are homol- 

 ogous partners in heredity. 



It was not until the beginning of the present century, after Mendel's 

 laws had been re-established and chromosomes had been discovered, 

 that sex was recognized as a hereditary trait in itself, dependent 

 principally upon genes. That other factors besides genes may con- 

 tribute to the determination of sex is no doubt true. For example, 

 Dr. Oscar Riddle, of the Carnegie Institution of Washington, has 

 advanced a well-grounded theory of the metabolic determination of sex, 

 based upon exhaustive experiments extending over many years, in 

 breeding doves at Cold Spring Harbor, Long Island. Other inves- 

 tigators have emphasized the modifying influence of the external 

 environment, and of the internal hormones, but no one denies the 

 action of the genes as the primary effective factor in sex determi- 

 nation. 



The theory most generally accepted today to account for the 

 approximate equality of the sexes in the offspring of any species is 

 that of Correns, who postulated that the gametes of one parent are 

 of two kinds, male-producing and female-producing, while the gametes 

 of the other parent are alike so far as sex determination is concerned. 

 This idea has been amply substantiated by the discovery in many 

 forms of plants and animals of what has subsequently been designated 

 as sex chromosomes. 



As has been repeatedly emphasized, chromosomes occur in homolo- 

 gous pairs, one member from each parent. McClung in 1902, dis- 

 covered that in the germ cells of the male locust, Xiphidium fasciatum, 

 there occurred an odd chromosome without a mate while in the 

 female immature germ cells every chromosome was supplied with a 

 corresponding mate. Consequently, this being the case, when the 

 members of the chromosome pairs, following synapsis, separate to 

 form the gametes, the odd chromosome joins one group of daughter 

 chromosomes, leaving the other group one chromosome short. The 

 former sort of gametes, carrying the odd chromosome, upon union 

 with a normal female gamete having a full quota of chromosomes, 



