70 THE SPRIKG GRAItf-APHIS OR " GREEK BUG. " 
Mr. T. D. Urbahns, of this bureau, carried on a series of check 
experiments at Dallas, Tex., in 1909, starting in March and ending in 
the fall. (See table, pp. 64-69.) As will be observed, and for 
reasons explained farther on, he did not obtain the sexes. By these 
experiments the maximum number of generations was secured as 
described under rearing methods (p. 51). The maximum number of 
generations in 1908 among the five series of continuous generations was 
21 and, as shown below, occurred in series I of first-born; the mini- 
mum being 6 in series FF of the series of last-born. The complete 
series are as follows: Series B, maximum (from first-born), 20 genera- 
tions; series BB, minimum (from last-born), 9 generations; series C, 
maximum (from first-born), 18 generations; series CC minimum 
(from last-born), 8 generations; series F, maximum (from first-born), 
16 generations; series FF, minimum (from last-born), 6 generations; 
series G, maximum (from first-born), 19 generations; series GG, 
minimum (from last-born), 9 generations; series I, maximum (from 
first-born), 21 generations; series II, minimum (from last-born), 10 
generations. If all of these be added, we will find the average to be 
13.6 generations. This will represent the approximate number of 
generations for the year. In 1909 there were two series reared, A and 
B, both resulting the same. Series A, maximum (from first-born), 
18 generations; series AA, minimum (from last-born), 7 generations; 
series B, maximum (from first-born), 18 generations; series BB, 
minimum (from last-born), 7 generations. The average for these 
two lines would give 12.5 generations, a little lower average than at 
Richmond, Ind. 
Mr. Urbahns carried out one series of first-born generation experi- 
ments at Dallas, Tex., in 1909, from which he obtained only the 
maximum number of generations. He began March 31 and finished 
November 3. In this time he reared through 25 generations but did 
not ascertain the sexes, neither was he successful in finding them in 
the fields. 
It appears that the species will vary in the number of generations 
produced from individuals hatched the same day, and from the off- 
spring kept under the same conditions throughout the year. This 
will readily be understood when the amount of individual variation 
in molting is considered. 
AGE AT WHICH FEMALES BEGIN REPRODUCING. 
The age at which females begin reproducing varies greatly between 
spring and summer and between fall and summer; as between spring 
and fall the age is very much the same. At Richmond and La Fayette, 
Ind., Toxoptera begins reproducing at from 5.9 to 16 days between 
the middle of May and latter part of September. From the time of 
hatching until the middle of May the period is from 20 to 27 days; 
