Heredity of Race-Characters in Silkworm (Bombyx mort) 763 
Series J, (Table IV) it shows a percentage value of 50 per cent" 
(see “Table of Descent’). 
SUMMARY 
An account is given of a series of breeding experiments extend- 
ing throughout five years, from the spring of 1904 through the 
summer of 1908. These experiments originated in a single 
cross of 1904 involving a female univoltin silkworm and a male 
pure bivoltin silkworm. 
The essential feature of the breeding is that matings were con- 
fined within series representing certain conditions of ancestry so 
that each lineage could be traced back to the original cross. and 
the different lineages compared. It is pointed out that each 
character is transmitted by either parent but finds expression 
through the female parent only. It is further pointed out that 
lack of expression of the characters in question is no indication 
that they have failed in transmission, that is, “‘transmission of a 
character has no relation to its expression.” 
It is noted that there is no uniform proportion such as is observed 
in Mend lian crosses between the characters in first and succeed- 
ing generations. On the contrary there is a noticeable fluctuation 
of prepotency from one character to the other as generations 
ensue. The univoltin is at first prepotent. As the hybrid uni- 
(bi) oltin generations increase the percentage of univoltins 
decreases. As the hybrid bi (uni)voltin generations increase the 
percentage of univoltins also decreases and much more rapidly. 
It is suggested that the past history of the characters probably 
has much to do with their present interrelation, that 1s, that the 
younger univoltin, though long selected cannot hold its own 
against the older bivoltin although it exhibits a perceptible pull 
for several generations. 
It seems that as between these intra-specific characters, there 
is an underlying “law of potency” that has to do with characters 
as ancestral rather than with characters as parental units. 
11 Note added September 20, 1909. In the summer of 1909 bivoltinism shows a percentage value 
of 67 per cent in this series. 
Bionomics Laboratory 
Stanford University, California 
June, 1909 
