HEREDITY OF THE RACE-CHARACTERS UNIVOLT- 
INISM “AND BIVOLTINISM IN THE SILKWORM 
(BOMBYX MORI) 
A CASE OF NON-MENDELIAN INHERITANCE 
BY 
ISABEL McCRACKEN 
‘In the spring of 1905, during the progress of certain breeding 
experiments with the silkworm (Bombyx mori) to determine 
the hereditary value of certain larval characters, an unlooked- 
for phenomenon occurred. ‘This was the hatching, some ten or 
fifteen days after the eggs were oviposited, of a number of broods 
of eggs that were supposed to be destined to lie over the winter 
and hatch in the following spring. 
During the month of April (1905) some 210 inter- and cross- 
matings were made between moths that had been reared through 
the spring from “recorded”? 1904 parents. After the matings 
were made, the mating boxes, small manilla paper boxes in 
which eggs were oviposited, were set aside to await removal to 
winter quarters. Ten days later the boxes were examined in 
order to remove the dead moths and to note the condition of 
the eggs. It was observed that the eggs represented two condi- 
tions. In many boxes, these had the gray appearanceof the 
normal univoltin egg. In six boxes, however, the eggs, though 
alive, were of a dull yellowish appearance. 
The univoltin race of silkworms produces but one generation 
during the year, a spring generation, from eggs that have win- 
tered. When first oviposited, the univoltin egg is yellow, very 
light yellow if the larva or silkworm is destined to spin a white 
cocoon, a much deeper yellow or golden if the silkworm is des- 
tined to spin a yellow cocoon. About 24 hours thereafter, the 
Tue JourNAL or ExPERIMENTAL ZOOLOGY, VOL. VII, NO. 4. 
