94 
together with that contained in the various tables and diagrams 
relating to temperature effects upon this insect: (1) That mild 
winters are of much more vital importance in Texas than they are 
in the latitude of southern Kansas and northward, and (2) that the 
influences of abnormally warm weather, if the temperature rises high 
enough, have the effect of bringing about activity among the parasites, 
which has a restraining effect upon the increase of Toxoptera. 
In the North, where the pest winters over wholly or largely in the 
egg stage, warm winters are of less importance, while abnormally 
cool weather during spring and early summer exerts a far greater influ- 
ence. This fact renders a study of the embryology and temperature 
effects upon eggs and stem mothers necessary to a full understanding 
of the entire problem, extending as it does over both North and 
South. 
The fact just stated is somewhat peculiar and was unexpectedly 
revealed by the combined studies of those engaged in the investiga- 
tion of the insect, and called for a study of the development of the egg, 
which has been carried on by the junior author with the results 
given in the following pages. The most important influence of 
temperature is, of course, upon the development of its principal 
natural enemy, ApJiidius testaceipes, further discussed in connection 
with the studies of that insect. 
EMBRYOLOGY. 
Although the development of the parthenogenetic egg in Aphididae 
has received considerable attention from several authors, that of the 
true egg has received very little study. Hence the junior author 
has given a limited amount of time to the study of certain important 
phases in the development of the winter egg, as contrasted with the 
winter condition of the viviparous insect in the South. 
Not wishing to duplicate the work of the other writers, who have 
confined their studies for the most part to the earlier stages of develop- 
ment, he has begun with the formation of the blastoderm, his main 
object being to follow the principal stages of development of the 
embryo through the fall until growth is checked by freezing tempera- 
tures, to note the time when growth is resumed in spring, and to 
observe the effect of varying temperatures on development, all of 
which has to do with the fluctuations of the insect in point of numbers 
in the North and relates to its economic importance, besides balancing 
our knowledge of the insect at a corresponding season in the South. 
Most of these studies were carried out at the University of Illinois 
under the supervision of Dr. J. W. Folsom. We are deeply indebted 
both to him and to Dr. W. M. Wheeler of Harvard University for 
their kindly criticisms and helpful suggestions. 
