ILLUSTRATIONS 
Page. 
Plate I. Fig. i. — Wheat field totally destroyed by the spring grain-aphis 
( Toxoptera graminum). Fig. 2. — Circular spot in wheat field where 
growing grain has been destroyed by the spring grain-aphis 32 
II. Fig. 1. — Stand on which experiments were carried out in rearing the 
spring grain-aphis. Fig. 2. — Area on grounds of the United States 
Department of Agriculture, at Washington, D. C, where the spring 
grain-aphis usually occurs on bluegrass in excessive abundance 
during summer 36 
III. Development of the embryo in the egg of Toxoptera graminum. 
Fig. 1. — Longitudinal section showing the blastoderm partly 
formed. Fig. 2. — Longitudinal section showing the thickening of 
the blastoderm about the ovarian yolk previous to invagination. 
Fig. 3. — Longitudinal section representing the germ band at the 
beginning of invagination folding inward about the ovarian yolk. 
Fig. 3a. — Section of the blastoderm. Fig. 4. — Longitudinal sec- 
tion of a more advanced stage of invagination, the germ band having 
almost closed over the ovarian yolk 100 
IV. Development of the embryo in the egg of Toxoptera graminum. 
Fig. 1. — Longitudinal section representing the somewhat cone- 
shaped germ band ready to release itself from the surface of the egg. 
Fig. 2. — Sagittal section representing the tubular germ band com- 
pletely submerged within the yolk. Fig. 3. — Transverse section of 
the germ band. Fig. 4. — Sagittal section showing the germ band 
folding and differentiating into amnion and germ band proper .... 100 
V. Development of the embryo in the egg of Toxoptera graminum. 
Fig. ] . — Sagittal section showing the germ band differentiated into 
three layers and folded almost upon itself. Fig. 2. — Surface view 
of Plate VI, figure 1. Fig. 3.— Surface view of Plate VI, figure 2. . 100 
VI. Development of the embryo in the egg of Toxoptera graminum. 
Fig. 1. — Sagittal section of the embryo, showing the segmentation. 
Fig. 2. — Sagittal section showing a much more advanced stage of 
growth than that of figure 1 100 
VII. Development of the embryo in the egg of Toxoptera graminum. 
Fig. 1. — Sagittal section showing the embryo in position to escape 
from the center of the egg. Fig. 2. — Sagittal section showing the 
embryo at the surface of the egg. Fig. 3. — Sagittal section, later 
stage of development. Fig. 4. — Sagittal section; dorsal organ im- 
mersed within the body cavity where it has begun to disintegrate. 
VIII. A lady-beetle enemy of the spring grain-aphis. Pupae of Hippodamia 
convergens attached to stem of cowpea and wheat straws in a field 
where the spring grain-aphis had been excessively abundant 128 
IX. Fig. 1. — Brush drag used by the junior author in experiments and 
also by farmers in destroying the spring grain-aphis in the fields at 
Hobart, Okla. Fig. 2. — Roller used in experiments by the junior 
author and by farmers in experiments in destroying the spring 
grain-aphis in Oklahoma 136 
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