748 Isabel McCracken 
egg changes to a muddy or dull yellow tone which soon gives way 
to a strawberry pink and later to a characteristic gray. 
The bivoltin race of silkworms produces two generations dur- 
ing the season. ‘The eggs of the spring moths fail to go into the 
gray resting condition of the univoltin egg but issue after ten or 
fifteen days, during which time they remain of the dull yellow or 
slightly pinkish appearance while the young embryo of the 
summer generation 1s developing. 
The occurrence of the bivoltin in the univoltin race is occasional 
but rare. In the thousands of broods that have been reared in 
our breeding rooms since 1903 it has occurred a number of times. 
Its occurence, [ look upon as a reversion to an ancestral condition, 
mainly from the fact that the most nearly allied wild silkworms 
of China aud India recorded by Rondot in “Les Soies” are 
bivoltin. Hutton! also gives some evidence for this view. As 
such, I am following up its behavior in heredity, for comparison 
with results herein recorded. It is hoped that further experimen- 
tation with this material will show what influence, if any, this 
known sporting or reversionary tendency of the univoltin race 
has upon the trend of heredity in experiments involving uni- and 
bivoltins. 
The experiments recorded in the present series were carried on 
with offspring of pure univoltin and pure bivoltin stock. 
The six masses of eggs of the 1905 lot of second generation 
hybrids that were noticed to remain in the dull yellowish condi- 
tion as previously noted were subjected to a day-to-day inspec- 
tion until, on the 13th and 14th days they were observed to hatch 
and a second generation or “summer” brood of larve appeared. 
Thus the significance of their not having entered the gray 
condition. 
The 1904 records of these six broods were then looked up. 
These records showed that in each of the six cases, one (the 
female) or both parents had come from the identical spring brood. 
The 1904 female parent of this spring brood was a univoltin 
salmon-colored cocooner from a banded or “zebra”’ larva reared 
1 Hutton Thomas: On the Reversion and Restorationof the Silkworm. Transactions of the Ents 
Soc. of London, p. n. s. vol. iv, 1864, pp. 143-173. 
