THE DETERMINATION OF SEX 329 



Gametogenesis occurs normally in the queen bee, consequently 

 her eggs contain the haploid number (16) of chromosomes. It 

 follows that the drones developed from these eggs have only the 

 haploid number although the queens and workers have the normal 

 diploid complex of thirty-two chromosomes. The production of 

 normal male gametes demands some compensating phenomenon, 

 which is found in the abortive reduction division. At this stage 

 all of the chromosomes pass into one spermatocyte so that all 

 spermatozoa receive the normal haploid number, and at fertiliza- 

 tion establish the normal diploid complex of the females. 



The Life Cycle of Aphids. This life cycle demands another type 

 of compensation in behaviour of the chromosomes. Sexual individ- 

 uals appear at intervals during the cycle, but they are separated by 

 long successions of parthenogenetic females. The stem mothers 

 hatch in the spring from fertilized eggs which have passed the 

 winter; no males appear at this season. The stem mother heads the 

 succession of parthenogenetic females, and in the fall males and 

 females appear which produce the winter eggs. The diagram 

 (Fig. 188) shows the behaviour of the chromosomes accompanying 

 these steps. The parthenogenetic eggs from which the males and 

 females develop are produced in one case by a normal mitotic 

 maturation division which results in one ovum and one polar 

 body. The egg in this case contains the same chromosomal com- 

 plex as the cells of the parent. In the other case one entire x 

 chromosome is extruded in the polar body, and consequently the 

 egg receives the odd number of chromosomes characteristic of the 

 male. In order that females alone may develop from the winter 

 eggs, maturation in the male is accompanied by degeneration of 

 the secondary spermatocytes which contain no x chromosome. 

 All spermatozoa therefore contain an x chromosome and the dip- 

 loid number is restored in every case by fertilization. 



Elimination of the Male. It is evident that the parthenoge- 

 netic production of females, which occurs in some insects and roti- 

 fers, might in extreme cases result in the limitation of reproduction 

 to this method. In such an Amazonian species males would be 

 superfluous, and this is a possible explanation for the failure of 

 biologists to discover the males of certain rotifers. The evidence 

 available is not, however, conclusive. 



Artificial Parthenogenesis. The occurrence of natural par- 

 thenogenesis in sexual organisms suggests that the stimulus of 



