. Elementary text-book of zoology. Zoology. BLASTOSPIIERE. 113 ment reach the periphery, and the fatty and often darkly-granular food yolk conies to constitute the central mass of the egg (Insects). As various as the forms of segmentation are the methods by which the segments are applied to the building up of the embryo. Fre- quently in cases of equal segmentation the segments arrange them- selves in the form of a one-layered vesicle, the blastosphere, the central cavity of which not rarely contains fluid elements of the food yolk ; or they are at once divided into two layers around a central
. Elementary text-book of zoology. Zoology. BLASTOSPIIERE. 113 ment reach the periphery, and the fatty and often darkly-granular food yolk conies to constitute the central mass of the egg (Insects). As various as the forms of segmentation are the methods by which the segments are applied to the building up of the embryo. Fre- quently in cases of equal segmentation the segments arrange them- selves in the form of a one-layered vesicle, the blastosphere, the central cavity of which not rarely contains fluid elements of the food yolk ; or they are at once divided into two layers around a central cavity containing fluid; or they form a solid mass of cells without. FIG. 107.—Six stages in the segmentation of a spider's egg(Philodromus limbatus) after Hub. Ludwig. A, egg with two deutoplasmic rosette-like masses (segmentation spheres); B, the rosette-like masses with their centrally placed nucleated protoplasm without egg membrane ; C, egg with a great number of rosette-like masses ; D, the rosette-like masses have the form of polyhedral deutoplasmic columns, each of which has a cell of the blas- toderm lying immediately superficial to it; E, stage with blastoderm completely formed ; F, optical section through the same. The yolk columns form within the blastoderm a closed investment to the central space. any central cavity. In numerous cases, especially when the food yolk is relatively abundant (unequal and partial segmentation) or the food supply continuous, the embryonic development is longer ami more complicated. The embryonic rudiment in such cases has at first the form of a disc of cells lying on the yolk; it soon divides into two layers, and then grows round the yolk. 8. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Claus, Carl, 1835-1899; Sedgwick, Adam, 1854-1913; Sinclair, F. G. (Frederick
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
