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 1st, 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 Eeports 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. 



