. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 440 BULLETIN OF THE After the formation of the second polar globule, which somewhat ex- ceeds the first in size, but is otherwise like, and formed like, the first the half of the spindle remaining in the egg contains a disk of granules and about its tip a homogeneous area and faint radial striations. A little later a cluster of vacuoles closely pressed together has taken the place of the granules of the disk. These vacuoles are sliarply limited from the yolk by a dark lustrous rind having the appearance of nu
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 440 BULLETIN OF THE After the formation of the second polar globule, which somewhat ex- ceeds the first in size, but is otherwise like, and formed like, the first the half of the spindle remaining in the egg contains a disk of granules and about its tip a homogeneous area and faint radial striations. A little later a cluster of vacuoles closely pressed together has taken the place of the granules of the disk. These vacuoles are sliarply limited from the yolk by a dark lustrous rind having the appearance of nuclear sub- stance, and in the contained fluid small dark granules are suspended. The vacuoles soon increase in size, and flow together into a simple, lobed body, — a nucleus. This female pronucleus migrates toward the centre of the egg, where it meets the male pronucleus. Meanwhile there have appeared in the last-formed polar globule numerous vacuoles in place of the granular zone which occupied its middle. These enlarge and unite into a single vacuole with a dark cortical layer, which stains in carmine. The first-formed globule is partially constricted into two. All three remain attached to each other, and, through the largest one, to the yolk, till about the time of the first cleavage, when they are all combined into a single flattened structure containing three bodies that stain readily. The formation of each polar globule takes place in the manner of a cell division, or, in view of the difference in size of the products, as a cell budding. Hertwig's studies on Rana are mostly confirmatory of the results reached by Van Bambeke. In the ovarian egg at the time the germi- native vesicle is growing most rapidly it presents a spherical form and complicated structure. There is a membrane and about a hundred nucleoli, which are in contact with its inner surface,"^ and a rich net- work of finer or broader bands of protoplasmic substance, whose function it is to nourish the nu
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Keywords: ., bookauthorha, bookcentury1800, bookdecade1860, booksubjectzoology
