FLUCTUATING VARIATIONS AND THEIR 



INHERITANCE. 



While such characters as larval pattern and cocoon color seem to 

 be essentially discontinuous in their appearance and alternative in in- 

 heritance, certain other silkworm characters are distinctly fluctuating 

 or continuous in variation and non-alternative in inheritance. Such 

 characters are amount and quality of silk thread composing the 

 cocoon, shape of the cocoon, wing-pattern of the adults, wing-venation, 

 certain larval markings subsidiary to the whole condition of color 

 pattern, degree of adhesiveness of the eggs, polyvoltinism, etc. 



A good deal of laborious work was done in the first three years 

 of the six over which our experimental rearing has extended, in con- 

 nection with these continuous or fluctuating variations. But little 

 space, however, need be given to stating the results of the work. 



Coutagne has already shown the strictly fluctuating character of the 

 differences in "richesse de sole," which may be taken as including the 

 quantity and quality of the silk. His series of rearings from matings 

 based on a careful selection as regards the character extend over 

 ten years and show clearly the variational and inheritance behavior of 

 the characteristic. It is strictly continuous, fluctuating, and non- 

 alternative. 



For a knowledge of the behavior in variation and inheritance of 

 the characteristic, shape of cocoon, Coutagne and Toyama's work is 

 sufficient. They both show it to be fluctuating as to variation and 

 non-alternative as to inheritance. 



Toyama has worked also on the character polyvoltinism, or, better 

 expressed, the brood character of the silkworm, whether of annual 

 generation, or of two or more generations a year, expressed by silk- 

 growers as univoltine, divoltine, multivoltine. He finds it to be a 

 fluctuating character, to be maintained in one condition only by rigorous 

 selection. "Thus," he writes, "when we crossed a multivoltine with 

 univoltine breed, the eggs laid by the moth were either pure maternal 

 or pure paternal, very rarely a mixture of both parents. Those forms 

 raised from the first cross do not remain true to the parents in subse- 

 quent generations. Even when we selected multivoltine parents for 

 five generations, we failed to get any constant multivoltine breed." 

 Miss McCracken has carried on and still is maintaining in our labora- 



