The Canadian oyster : its development, environment and culture . e pole of that hemi-sphere of the egg which becomes the larger. Those rays which lie alongthe axis between the two centrosomes form a nuclear spindle, and by con-traction the chromosomes are divided into two groups. One of thesegroups is thrust outwards, carrying with it portions of an astrosphere,protoplasm and egg-membrane, which constricts around and separatesthe mass as a small globule (first polar globule) on the surface of the rela-tively large egg (fig. 7). A nuclear spindle is reconstructed within the egg,the chromosomes
The Canadian oyster : its development, environment and culture . e pole of that hemi-sphere of the egg which becomes the larger. Those rays which lie alongthe axis between the two centrosomes form a nuclear spindle, and by con-traction the chromosomes are divided into two groups. One of thesegroups is thrust outwards, carrying with it portions of an astrosphere,protoplasm and egg-membrane, which constricts around and separatesthe mass as a small globule (first polar globule) on the surface of the rela-tively large egg (fig. 7). A nuclear spindle is reconstructed within the egg,the chromosomes again divided, and a second polar body soon formedat the base of the first (fig. 8). In the eggs of some animals it has beenobserved that the chromosomes become split longitudinally into doubletheir number during the formation of the first polar body, and that thispolar body divides, each part taking half the chromosomes during theformation of the second polar body. This would seem to show that the COMMISSION OF COXSERVATIOX Plate I ^im y^ ^g 1^0 i^ a l0<». Egg—Embryo—Larva—to youngest spat(Enlarged 150 times) KEY TO PLATE I All the figures of this plate are drawn as accurately as they admit of,lu the same scale of magnification, viz., 150 diameters, so that the relativesizes of different stages may be seen at a glance. They are also orientedin the same position throughout, with the dorsal margin upwards and theanterior end to the observers right, , they lie on the left side like theattached 03^ster. Fig. 1. Oysters ovum. Oc. 5, ol)j. 4 = 7-5 of the ocular micrometerscale, of which each unit in terms of the known stage micrometer is Q-9/^. 7-5 X 6-9= 51-75/^= •05mm. (•05^25= -002 inch = 1/500 inch). •05 X 150=7^5 mm=the size of the figure. Figs. 2-8. Segmentation and formation of the embryo. Figs. 9-21. The larva. Fig. 22. The youngest spat. Fig. 2. Extrusion of the first polar body and lengthening of theoosperm. Fig. 3. First (partial) cleavage into two bla
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectoysterc, bookyear1913
