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Development of the Embryo in the Egg of Toxoptera graminum. 



Fig. 1. — Longitudinal section showing the blastoderm partly formed, being farthest advanced in the anterior region. The mass of ovarian yolk is lodged at the posterior 

 pole. Figures la and lb represent the yolk cells magnified !S45 diameters. Fig. 2. — Longitudinal section showing the thickening of the blastoderm about the ovarian yolk 

 previous to invagination. Magnified 156 diameters. Fig. 3.— Longitudinal section representing the germ band at the beginning of invagination, folding inward about 

 the ovarian yolk. Magnified 156 diameters. Fig. 3a.— Section of the blastoderm. Magnified 430 diameters. Fig. 4. — Longitudinal section of a more advanced stage of 

 invagination, the germ baud having almost closed over the ovarian yolk. Magnified 15a diameters. (Original.) 



