SEX AND GENES 211 



bia pineti an unpaired chromosome is not visible in the 

 female or in the male, nor is an unpaired chromosome 

 visible in several other moths. On the other hand, in 

 Phragmatobia fuliginosa there is a compound chromo- 

 some containing the sex-chromosome. In the male there 

 are two of these present; in the female only one is com- 

 pound like those of the male. It seems not improbable 

 that this relation may also exist in other moths where the 

 W-element and the Z-elements do not appear as separate 

 chromosomes. 



Another demonstration of sex-linked inheritance in 

 moths has been given by Federley in a cross between two 

 species of moths (Pygaera anachoreta and P. curtula). 

 This case is interesting because within each species the 

 male and female caterpillars are alike. They show specific 

 differences, however, when the caterpillars in the two 

 species are compared. This specific difference, that is not 

 dimorphic within the species, becomes the basis for a 

 sexual dimorphism in the F x caterpillars (when the cross 

 is made "one way"), because, as the results show, the 

 main genetic difference between the caterpillars in the 

 two races lies in the Z-chromosomes. When anachoreta is 

 the mother and curtula the father, the hybrid caterpillars, 

 after the first molt, are markedly different. The hybrid 

 male caterpillars are closely similar to those of the mater- 

 nal race (anachoreta), while the hybrid female caterpil- 

 lars resemble those of the paternal race (curtula). 



The reciprocal cross gives offspring that are all alike. 

 These results are explicable on the assumption that the 

 anachoreta Z-chromosome carries a gene (or genes) 

 dominant to the gene (or genes) in the Z-chromosome of 

 curtula. The special interest in this case is due to the 

 genes in one species acting as a dominant to allelomor- 

 phic genes in the same chromosome of the other species. 

 The analysis of the result can be carried over consistentlv 



