OTHER METHODS OF SEX-DETERMINATION 241 



^dduals which are called females and males since they 

 produce eggs and sperm-cells respectively. 



In criticism of these statements it may possibly be said 

 that the facts have only been restated and not explained. 

 This is quite true. All that has been attempted is to point 

 out that the facts may be restated in such a way that 

 there is no apparent contradiction involved in the tw^o 

 cases. We may look forward perhaps to the time when the 

 number and nature of the genes involved in cases where a 

 difference of balance produces two kinds of individuals, 

 will be determined. Meanwhile there is nothing in the 

 situation that need cause anxiety, and certainly nothing 

 that can be used as a refutation of recent advances in an 

 understanding of sex-determination. 



The haploid condition in animals is characteristic of the 

 gametes. There are no cases of alternating haploid and 

 diploid generations as in plants. But there are two or three 

 types at least in which one sex is diploid and the other 

 haploid. In the Hymenoptera and a few other insects the 

 female is diploid and the male haploid, at least in the early 

 stages of development. In Eotifera the females are diploid 

 and the males are haploid. There is no evidence in either 

 group of sex-chromosomes as such. At present no explana- 

 tion resting on experimental evidence can be offered to 

 explain these relations. Until such evidence is forth-com- 

 ing the possible theoretical interpretations that have been 

 suggested are not illuminating. 



In Drosophila on the other hand where a known sex 

 mechanism is at hand, and where there is experimental 

 evidence bearing on the problem of balance of the genes 

 involved in sex-determination, there is a recent observa- 

 tion by Bridges that is significant. Two mosaic individuals 

 were found which, from genetic evidence, seemed probably 

 to be composites, in part haploid and in part diploid. In 

 one case the haploid region includes the location of a sec- 



