HAPLOIDS 149 



present in all cells of the embryo. In the maturation 

 stages of the germ-cells of the male, there is no evidence 

 of a reduction division (not even a rudimentary process 

 as in the bee) and the equational division, if it is present, 

 does not differ from the earlier or oogonial divisions. 



There is some evidence that the unfertilized eggs of 

 lice develop into males, as suggested by the breeding 

 experiments of Hindle. In one of the mites, Tetranychus 

 bimaculatus, the unfertilized eggs produce males, the 

 fertilized, females (Perkins, H. A. Morgan, Bank, Ewing, 

 Parker). It has been shown by Schrader that the males 

 are haplonts with only three chromosomes, the females 

 are diplonts with six chromosomes. The early ovarian 

 eggs have six chromosomes that conjugate to give three 

 bivalents. Two polar bodies are given off, leaving three 

 chromosomes in the egg. If the egg is fertilized three 

 chromosomes are added, giving six in the female, if the 

 egg is not fertilized it develops directly into a male with 

 three chromosomes in each cell. 



Virgin females of one species of thrips, Anthothrips 

 verbasci, examined by A. F. Shull, produce only males 

 from unfertilized eggs. These males are probably hap- 

 lonts. 



In mosses and liverworts the protonema and moss 

 plant stage (gametophyte) are haplonts. Wettstein has 

 by artificial means brought about the doubling of the 

 number of chromosomes in cells of the protonema and 

 from these has obtained diploid protonema and moss 

 plants. This result proves that the difference between 

 this stage and the sporophyte stage is not due to the num- 

 ber of chromosomes that each contains but is a develop- 

 mental phenomenon in the sense that in order to reach 

 the sporophyte stage the spore must pass through the 

 gametophyte condition. 



