GENETIC STUDIES ON THE SILKWORM 
occurring in the male and female alike. 
Saunders (191 o, 191 1 ) concludes from her elaborate researches on the 
doubling character in the flower of Petunia and MaUhiola that there is a 
sexual dimorphism of gametes occurring in a way that she describes as follows : 
" although both in the single Stock which constantly throws 
doubles, and in the single Petunia which yield doubles when fertilized by 
a double, the pollen is homogeneous [ovules heterogeneous] in respect of 
some factor needed to produce singleness, the homogeneity is brought 
about by the absence of this factor in the Stock, by its presence in 
Petunia." (1910, p. 63.) 
Thus in the Stock the female gametic series was assumed as n-i XY : i 
Xy : 1 xY : n— i xy, and the male gametic series as xy, where X and Y stand 
for the factors necessary for the manifestation of singleness. 
Goldschmidt (1913b) discussed this case and endeavoured to analyse it as 
an example of sex-limited inheritance, but Saunders (191 3) contends for her 
own position. In fact the total sterility of one (Petunia, female) or both 
sexes (MaUhiola) of recessive (double-flowering) plants renders a direct test 
of gametic distribution difficult. 
Morgan and his collaborators found in Drosophila. a number of cases in 
which male and female gametic series were decidedly different, that is the 
linkage is partial in the female and complete in the male. This case is, there- 
fore, the only instance known so far, which shows a close resemblance to 
the present case in Bombyx. In both the fruit-fly and the silkworm, the gametic 
series were tested not only by inbreeding, but also by reciprocally crossing 
the diheterozygotes with double-recessive individuals ; the results were in 
accordance in many respects in both cases. A notable contrast is however 
presented by these two species of the Insect, in that complete association 
took place in the male in the fly but in the female in the silkworm, while 
partial association occurred in the female of Drosophila and in the male of 
Bombyx. 
The said difference strongly reminds us of two kinds of sex-limited 
