546 THE POPULAR SCIENCE MONTHLY 



when the other combination occurs, 18 chromosomes from egg and 17 

 chromosomes from sperm, an organism results that has only 35 chro- 

 mosomes, and this is a male. It seems, therefore, as if the accessory 

 chromosome was a sex-determinant in some sense — probably only in 

 the sense of a visible accompaniment of some hidden underlying physi- 

 ological cause of sex — perhaps as the carrier of a specific enzyme or 

 '' hormone." 



To bring these facts into line with Mendelian principles it becomes 

 necessary to postulate (1) two kinds of eggs, just as there are two kinds 

 of spermatozoa, (2) selective fertilization, and (3) dominance of female- 

 ness, and the observed facts can be explained. If the accessory chromo- 

 some is a sex-determinant, then when an egg is fertilized by a sperm 

 lacking this element, the egg itself must carry the factor that determines 

 that the sex of the resulting organism of 35 chromosomes shall be a male. 

 In the event of the other possible combination the egg selected must 

 have been one carrying the female determinant and, since the accessory 

 chromosome is a male-determinant and the union of the two produces 

 a sex-hybrid, femaleness must dominate in order to yield a female or- 

 ganism of 36 chromosomes. 



The most recent position is that of Dr. Correns, professor of botany 

 in the University of Leipsig, to the effect that there is only one kind of 

 egg (always female) and two kinds of spermatozoa. He has brought 

 forth facts to amply support this view in flowering plants. He shows 

 that the spermatozoa determine the sex and that the time of this deter- 

 mination is the instant of fertilization. Correns attempts to bring the 

 second position above mentioned into harmony with his own, and the 

 facts upon which Beard's position is based are given a reasonable inter- 

 pretation. We shall consider these various positions from Correns's 

 standpoint, and will note how he disposes of the obstacles above re- 

 ferred to. 



There are now known about one hundred cases, mostly among the 

 air-breathing arthropods, where there is a dimorphism of spermatozoa. 

 But if fertilization determines the sex, what about such cases where 

 eggs develop without fertilization, as in the drone honey-bee, ants and 

 plant lice (aphids and phylloxerans) ? These several examples until 

 recently had been serious stumbling-blocks to the theory that sex is 

 dependent on a dimorphism of spermatozoa. ISTor is the matter yet as 

 clear as we could wish it to be. All the fertilized eggs of the honey- 

 bee develop into females (workers or queens, depending upon the kind 

 and amount of food they receive), the unfertilized eggs develop into 

 males or drones. Meves has recently found that while the drone 

 honey-bee produces two kinds of spermatozoa, one set, the male-pro- 

 ducing, degenerates and becomes non-functional. Hence all fertilized 

 eggs must develop into females. The facts become intelligible if we 



