VISIBLE AND 



INVISIBLE CHARACTERS IN SILKWORMS. 



139 



(2) Out of 26 layings of pure multivoltine Nistri 2 s and 6 s ■ 

 all the eggs hatched, thus all being multivoltine. 



These results give a clue to the gametic, composition of the F 2 

 moths, for they show : — 



(1) that 19 F a £s were dominant in the univoltine character 

 and 2 in the multivoltine character. 



(2) that all the F 2 <$ s which may have been univoltine were 



recessive in the univoltine character. 



Table 3, illustrating descent of the univoltine and multivoltine 



CHARACTER IN THE CROSS BETWEEN THE UNIVOLTINE ItAL.-JaP. £ 



and Multivoltine Nistri <$ . 



Univoltine Ital.-Jap. $ X Multivoltine Nistri $ P x 



Layings all univoltine F\ 



11 ? moths 21 $ moths. 



7 layings univoltine. 2 multivoltine. 1 half multivoltine jP 2 



62 £ s. 34 $ s. 



37 layings univoltine. 2 almost univoltine. 2 multivoltine. 2 almost multivoltine. F 3 



34 ?s. 47 <Js. 



14 layings univoltine. 7 almost univoltine. 4 almost multivoltine F 



(Discontinued.) 



Unequal Sex-ratios. 



I had noticed that in the earlier generations of the Nistri $ 

 and Ital.-Jap. ^ cross (which were reared a year previous to that 

 of the Ital.-Jap. $ and Nistri J cross), the number of males 

 and females seemed very unequal, and that in one generation 

 males predominated, and in another, females. However, these 

 remarkable fluctuations gradually decreased in the latter 

 generations. 



In my second series of experiments, which were with the Ital.- 

 Jap. 2 ana * Nistri $ , I noted the exact number of males and 

 females in each generation, and found that in this reciprocal cross 

 the sex-ratios were also very unequal, but just the reverse in the 

 character of the predominating sex, for in ¥ A of the Nistri 5 

 cross there were many more females than males, while in F of 

 the Ital.-Jap. $ cross there were more males than females. 



The unequal sex-ratios could be accounted for by supposing 



