. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. ADAPTATION IN CLEAVAGE. 6l. Fig. i6. — Unio. Outline of section in the direction of the line ruled across Fig. 15 ; to show the elon- gation of the sphere-substance. elongated greatly in a horizontal direction, at right angles to the line uniting the germ-nuclei (Fig. i6)j and has thus marked otit the direction of the first cleavage-spindle. Nozv this elongation has begun, and the plane of division is indi- cated before the germ-nuclei have met. It might very readily be assumed that the plane of
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. ADAPTATION IN CLEAVAGE. 6l. Fig. i6. — Unio. Outline of section in the direction of the line ruled across Fig. 15 ; to show the elon- gation of the sphere-substance. elongated greatly in a horizontal direction, at right angles to the line uniting the germ-nuclei (Fig. i6)j and has thus marked otit the direction of the first cleavage-spindle. Nozv this elongation has begun, and the plane of division is indi- cated before the germ-nuclei have met. It might very readily be assumed that the plane of the first cleavage is deter- mined by the copulation- path of the germ-nuclei, as is stated to be the case in the ova of some other ani- mals (frog, Roux ; Toxo- p7ieiistes, E. B. Wilson). But whoever should take this position for Unio would have to explain how it happens that the sphere-substance elongates in the plane of the first cleavage-spindle before the germ-nuclei come together. It would be necessary, I believe, to assume that the distant sperm-nucleus ex- ercises an influence on the direction of migration and of elongation of the sphere- substance in the first cleav- age, but that, in the next division, the sphere-sub- stance acts independently; and this assumption is ab- surd on the face of it. The first cleavage-spindle forms in the centre of the. 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 Marine Biological Laboratory (Woods Hole, Mass. ). Boston, Ginn & Co
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectbiology
