544 Edmund B. Wilson. 



idiochromosomes in place of an unpaired heterotropic chromosome. 

 In all of these forms, as I showed in my first paper, the spermato- 

 gonial groups show fourteen chromosomes that may be equally 

 paired with the exception of a small and a large idiochromosome. 

 The oogonial groups in these forms also show fourteen chromo- 

 somes, but all may be equally paired, the small idiochromosome 

 being represented by a larger one that has a mate of equal size. 

 In these forms, accordingly, males are produced as a result of 

 fertilization by spermatozoa containing the small idiochromosome, 

 females by fertilization by spermatozoa containing the large idio- 

 chromosome (which accords with Stevens' result in Tenebrio). 

 This proves the correctness of my conclusion that the size-reduction 

 and final disappearance of the small idiochromosome has taken 

 place in the male sex only, and that the large idiochromosome 

 corresponds to the heterotropic chromosome. Complete disap- 

 pearance of the small idiochromosome in the male has led to 

 each a condition as exists in Anasa and other forms possessing a 

 heterotropic chromosome. These facts will be described and 

 discussed in the third of these studies. 



October 4, 1905. 



