62 Trans. Acad. Sci. of St. Louis. 
females deposited their first eggs between June 9 and 26. 
Our principal object in this work was to see whether or 
not the eggs which were laid on different days required 
the same length of time for their development, whether 
the first eggs deposited have the same period of incuba- 
tion as do the last eggs. In the notes already referred to 
we found this time to be the same for all the ova of 
each female, whether they were laid on the first or on 
the last day of her oviposition, and in the few cases where 
fluctuation occurred in the eggs of an individual, the 
variation was within one day. We therein suggested 
that when such variation occurred it may have been due 
to climatic variations. 
The same problem was pursued in 1912-13 on the four 
species of Saturniids herein dealt with. The results of 
the work are summarized in the tables below, which show 
the number of days required for the hatching of each 
female’s eggs deposited on the Ist, 2nd . . . 8th day 
of oviposition. (See Tables 35, 36, 37, 38.) 
For all of the four lots of Cecropias we find the dura- 
tion of incubation to be from 12 to 16 days. As a rule 
one finds no variation due to their early or late deposi- 
tion. 
What a striking difference there is between the period 
of incubation of these four lots, with a mode of 14 days, 
and the lot of 1911, in which the period was only 6 to 11 
days, with the mode at 8 or 9 days. We can account 
for the radical difference only by the fact that the eggs 
of the 1911 lot were laid a whole month later in the 
year than those of the present study. Inspection of 
the United States Meteorological Reports for these two 
periods when the eggs were incubating reveals that the 
mean temperature for June, 1911, was 79° F., while that 
of May, 1913, was 67.5°. So the cause of this difference 
may be only a matter of climatic conditions; the eggs 
laid at a warm time late in the season hatched much 
sooner than those exposed to the colder air earlier in 
the spring. 
