VISIBLE AND INVISIBLE CHARACTERS IN SILKWORMS. 



137 



From the results obtained it will be seen that all the eggs in 

 the layings of the multivoltine Nistri $ when crossed with the 

 univoltine Ital.-Jap. <$ hatched, i.e., the layings were all 

 multivoltine, whilst the univoltine paternal parent had no visible 

 effect on the character of the layings. This showed that the 

 multivoltine character was dominant in the $ , but recessive in 

 the S . Toyama, the Japanese authority on silkworms, also 

 found that in crossing pure breeds the first cross always resembled 

 the maternal parent. 



I usually found that the completely multivoltine layings did 

 not give the most multivoltine results as might be expected, but 

 the half multivoltine laying produced the least number of 

 univoltine layings in the long run. 



In the Nistri $ and Ital.-Jap. d 1 cross I discarded the 

 multivoltine layings which appeared in the earlier generations, 

 and mostly selected from the half, or partly multivoltine layings, 

 till in F 8 when most of the layings were almost entirely multi- 

 voltine. Some of the families have been entirely multivoltine 

 since F g , others have had a few partly univoltine layings, but in 

 none of the generations since F 4 have any of the layings been 

 entirely univoltine. 



Toyama does not give any detailed account of the results he 

 obtained in the brood characters. It would have been interesting 

 and useful, as the inheritance of these invisible characters appears 

 to be complicated. He selected from multivoltine forms, but 

 does not say if they were entirely or partly multivoltine. He 

 states as follows : — " Those forms raised from the first cross do 

 not remain true to the parents in subsequent generations. Even 

 when we selected multivoltine forms for five generations we failed 

 to get any constant multivoltine breed." 



In his. interesting pamphlet "Sulla riproduzione degli Incroci" 

 Dott. Quajat, when referring to his experiments with bivoltine 

 and univoltine races, states that " nelle successive riproduzioni, 

 bivoltinismo tende a diminuire, ed alcune volte anzi a scomparire 

 completamente. Sara oria interessante con sta tare se le ovature 

 ottenute univoltine, abbiano alio stato lateute il bivoltinismo, e 

 se questo si potra manifestare in seguito a nuovi incroci o 

 spontaneamente." 



I found that from F 8 the layings began to show a great 

 tendency to become completely multivoltine, and in those of the 

 F u moths, from which F 15 worms hatched, only one laying out of 

 the whole generation was half univoltine, all the others were 

 completely multivoltine. 



To account for the 22 layings in F„ appearing univoltine, the 

 univoltine character must have dominated in the maternal parents 

 of these layings. When a female F l was crossed with a " pure " 

 multivoltine Nistri only 3 eggs out of 250 hatched, and from 

 the results obtained, in the reciprocal cross, it was found that if 

 the maternal parent was a pure univoltine none of the eggs 

 hatched for about a year, and if she was a pure multivoltine all 



