Guide to the study of insects and a treatise on those injurious and beneficial to crops, for the use of colleges, farm-schools, and agriculturists . each to the surface, so that it appears darker thanthe other parts of the egg. This cellular layer is soon resolvedinto the blastoderm, or germinal layer, which thickens andnarrows, forming a longitudinal band. This is the lirst stageof the embryo, which lies as a thin layer of cells upon the outersurface of the jolk. Both ends of the body are alike, and weshall afterwards see that its back lies next to the centie of theegg, its future ventral sid
Guide to the study of insects and a treatise on those injurious and beneficial to crops, for the use of colleges, farm-schools, and agriculturists . each to the surface, so that it appears darker thanthe other parts of the egg. This cellular layer is soon resolvedinto the blastoderm, or germinal layer, which thickens andnarrows, forming a longitudinal band. This is the lirst stageof the embryo, which lies as a thin layer of cells upon the outersurface of the jolk. Both ends of the body are alike, and weshall afterwards see that its back lies next to the centie of theegg, its future ventral side looking outwards. The embryo isthus bent on Itself backwards. In the next stage the blastoderm divides into a certain num-ber of segments, or joints, Avhich appear as indentations in thebody of the embryo. The head can now be distinguished fromthe posterior end chiefly by its larger size, and both it and thetail are folded back upon the body of the embryo, the headespecially being sunk backwards doAvn into the yolk-mass. In a succeeding stage, as we have observed in the embryo ofDiplax, a Dragon-fly (Fig. 57), the head is partially sketched.
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectinsects
