74 £HE SPRING GRAIN-APHIS OR " GREEN BUG. 
91 
Toxoptera, in all probability, would not fall far behind these 
figures and the number might even be greater. Be that as it may, 
the illustration will suffice to show us that Toxoptera, with such 
remarkable powers of reproduction, could easily overrun the whole 
country if not checked in some manner. 
At Richmond and La Fayette, Ind., the maximum number of 
young produced in 24 hours was 8 in June, July, and August. The 
maximum number of young produced by any individual was 93, in 
the month of July. In Texas Mr. Urbahns found the maximum in 
24 hours to be 10 young in May, and the total number of young for 
one individual reached as high as 84 during the same month. 
At Richmond and La Fayette, Ind. , considering the progeny from only 
the individuals of the line of first-born generations, the average num- 
ber of young for the summer falls below either spring or fall, the spring 
being in the lead. When both the individuals from the line of first 
and last born generations are considered, those of the fall average 
less than those of the spring or summer. In 1908 the evidence was in 
favor of the line of first-born generations as being more prolific than 
the individuals of the line of last born. In 1909 the line of last-born 
generations held its own, especially in the spring and summer, falling 
behind slightly in the fall. In fact, in each line of generation experi- 
ments, the last born fall behind in average number of young in the 
autumn. Also, if an average be taken of the first and last born sepa- 
rately, the latter will fall behind. Considering each individual of 
both lines in all generations, both first and last together, the results 
are as follows: The maximum number of young produced by those 
born from March to the middle of June is 69, the average number for 
each individual for this period being 30.3; the maximum for those 
born from the middle of June until the middle of August is 93 young, 
the average number for each individual being 25.3; the maximum 
for those born after the middle of August is 66 young, the average 
for each individual being 24. 
The average number of young, including every individual under 
observation, whether connected with the generation experiments or 
otherwise, for the entire viviparous breeding season, of the years 
1907, 1908, and 1909, beginning the last week in March and continuing 
until November, both inclusive, is 28.2; there being 216 individuals 
used to obtain this average. 
In the generation experiments were a number of individuals that 
produced from 1 to 10 young and then disappeared, apparently not 
dying from natural causes. All of these were included, however, in 
arriving at the final average, as any average obtained by excluding 
one or more individuals from any cause whatever would be more or 
less arbitrary, since in nature the mortality, in all probability, would 
be much greater. All of the rearings were carried on out of doors, 
