(seven days); of the seventh, July 24 (fourteen davs); of the 
eighth, August o (twelve days); of the ninth, August 15 (ten 
days); of the tenth, August 25 (ten days); and of the eleventh 
September o (twelve days). On the 16tli of September males 
of the autumnal generation appeared, belonging probably to 
the twelfth generation from the egg. 
From the above account it will be seen that while the first three 
generations have an average life of nineteen days, the fourth to 
the twelfth followed each other at an average interval of preciselv 
eleven days. Many of our observations show that a much 
earlier start and a more rapid growth are common, and that 
a greater number of generations may consequents occur Thus 
although m the above account the stem mothers^ hatched April 
-4, we have collected young of this generation as earlv as April 
10; and our breeding records show that adults of this first 
generation may mature and young migrants may be born by 
pril -o, a date more than a fortnight earlier than those used 
above. Adult (winged) migrants have been seen by us May 11— 
again more than a fortnight earlier than the correspond^ 
date just mentioned. Further, we have had young of the third 
generation May 13, if we may trust an unverified report of Mr. 
Ai VV- Mally, who assisted me on this work in 1890. On the 
other hand as 1 have counted generations from first-born to 
first-born, the life of a generation is here made too short for 
the 
average. 
No special attempt was made to determine the number of in- 
dividuals a single female may produce or the relative produc¬ 
tiveness of the various successive generations. The fact is how¬ 
ever worthy of record that a single stem mother placed on a 
corn root in a breeding cage May 4, brought forth her first 
young May 6 and her twelfth and last May 15. At this time 
tlie first- born was a pupa, acquiring wings on the 19th The 
stem mother lived until the 22d, and was then placed in al¬ 
cohol. Another female of a midsummer brood brought forth 
fifteen young.* 
According to the results of experiments conducted for the 
purpose of determining the number of moults of the corn root 
aphis, and the intervals between successive moults, we find that 
two hundred and thirty miles lorn? 1 s? nne A be , 1 [t or strlp t ? n feet wide and 
a constant and often MdeoS evGn Sligbtly favorable * are 
