ILLUSTRATIONS. 



PLATES. 



Page. 

 ]?late L Fig. 1. — 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 snowing 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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