236 THE THEORY OF THE GENE 



polar bodies. The egg nucleus is left with the haploid 

 number of chromosomes. In the fertilized eggs the sperm 

 brings in a haploid set of chromosomes, which, uniting 

 with the egg nucleus, gives the diploid number. From 

 these eggs females develop (queens or workers). The 

 queens owe their more complete development to the food 

 supplied to the larvae in the queen-cells. This food is 

 different from that given to the larvae in the worker-cells. 

 The males (drones) are, as has been said, haploid.* 



In this case, the determination of sex cannot be sup- 

 posed to be due to any effect preceding maturation. There 

 is no evidence that the presence of the sperm-nucleus in 

 the egg affects the way in which the maturation division 

 of the chromosomes takes place. Furthermore, there is 

 no evidence that the environment (drone-cell or worker- 

 cell) has any effect on the course of development. There 

 is, in fact, no evidence here that any particular set of 

 chromosomes has been set apart as sex-chromosomes. 

 The only known difference between the two kinds of indi- 

 viduals, females and males, is the number of chromo- 

 somes present. We can, at present, only fall back on this 

 relation as the one that is in some unknown way corre- 

 lated with sex-determination. At present it cannot be 

 satisfactorily brought into line with other cases in in- 

 sects, where sex is related to a balance between genes in 

 the chromosomes, but it may still be due to a balance be- 

 tween the chromosomes (genes) and the cytoplasm. 



There is one further fact that involves sex-determina- 



4 It is known that, as the cleavage of the unfertilized egg of the male 

 proceeds, each chromosome breaks into two parts (except possibly in the 

 nuclei that pass into the germ-track). This process does not appear to be a 

 "division" of each chromosome, but rather its breaking or separating into 

 two pieces. If this interpretation is correct there is no actual increase in 

 the number of the genes and the occurrence of this process (also known in 

 some of the nematodes) does not throw any light on the question of sex- 

 determination. 



