NUMBER OF GENERATIONS PER YEAR. 63 
BIRTH OF YOUNG. 
In the fall of the year 1907 adult individuals of Toxoptera were 
brought from out of doors into a warm room, placed under a micro- 
scope, and observations made on the manner of birth of the young. 
The embryonic young within the body of the parent are inclosed 
within a thin, transparent, structureless membrane that corresponds 
to the vitelline membrane in the true egg. Normally, in warm 
temperatures, the young Toxoptera frees itself from this enveloping 
sac during birth. At a temperature of about 60° F. or below, the 
young are oftentimes dropped before they free themselves from the 
sac. In this latter case, upon landing upon the surface of the leaf 
they expand and contract gently until the sac is ruptured at the 
cephalic extremity and they are freed from their prison. 
NUMBER OF GENERATIONS PER YEAR. 
During the summer of 1907, at Richmond, Ind., a study of the 
continuous generations of this species was begun and followed 
through until December 10, the sexual forms and eggs being secured 
from bluegrass in the fields in October. With some of the young 
that hatched from these eggs (stem mothers) March 27 five lines of 
continuous-generation studies were begun and continued until the 
appearance of the sexes and eggs in the fall. These eggs were 
carefully retained and taken to Lafayette, Ind., where, upon their 
hatching on the first day of the following April, two more lines of 
continuous-generation studies were begun and continued until ended 
by the appearance of the sexes and eggs in the fall of 1909, as was 
the case in 1908. 
