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. 



