. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CYTO-EMBRYOLOGY OF SEA URCHINS. I 65 transparency of the blastomeres, this space can be photographed through the cell bodies. Figure 10, shows such a large space and it also shows how the "rims" of cytoplasm are encircling the fluid space. The surface view at the junction of the four blastomeres is shown in Figure 11. 4) Inflation of the hyaloplasmic envelope and a consequent dispersal of the blastomeres. If 4- to 16-celled embryos of Mespilia from which the fertilization membranes have been removed are put into 50
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CYTO-EMBRYOLOGY OF SEA URCHINS. I 65 transparency of the blastomeres, this space can be photographed through the cell bodies. Figure 10, shows such a large space and it also shows how the "rims" of cytoplasm are encircling the fluid space. The surface view at the junction of the four blastomeres is shown in Figure 11. 4) Inflation of the hyaloplasmic envelope and a consequent dispersal of the blastomeres. If 4- to 16-celled embryos of Mespilia from which the fertilization membranes have been removed are put into 50% or 70% sea water,, the hyaline plasma layer becomes inflated to a great extent and the blastomeres are carried with it away from each other. Figure 12 shows that, in spite of the volume increase of the blastomeres in the hypotonic medium, the cells are widely separated from one another. The dilution in the salt concentration obviously causes a softening of the hyaloplasmic gel. Such a decrease in the tensil strength of the layer would result in an increase in equilibrium volume even when the contained colloid remains con- stant in amount. The softening of the gel is further attested to by the fact that the hyaloplasmic layer under these conditions deviates from a spherical shape, owing to the pull by the FIGURE 12. Four-cell stage of Mespilia ylobnlns put in 50% sea water. The hyaloplasmic envelope is softened and expanded. The blastomeres are carried away from each other as the envelope enlarges. 5) Experimental induction of a lens-shaped space between the blastomeres. In the eggs of Strongylocentrotiis pulcherrimus, the amount of the fluid which ac- cumulates between the blastomeres during the interkinetic stage of the two-cell stage is not so large as in the case of Mespilia globnlus. As a result, the two blastomeres are nearly always touching at the cleavage plane (Fig. 13). If the adherence between the hyaline plasma layer and the blastomere surface also ex
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
