. The Biological bulletin. Biology; Zoology; Marine biology. MID-BODIES AND CENTRAL BODIES 575 present when the polar bodies are pinched off, but not when the egg divides. Crepidula eggs (ConkHn, 1902) show striking differences in mid- body structure from cycle to cycle. In first polar body figures it is a ring, which appears as two dots when seen in cross-section (Figs. 35 and 36); in the second, it is a smaller ring with a dot in it (Fig. 37), or just a dot (Fig. 38); in first-cleavage figures it is a large area containing a vesicle (Fig. 43); in third-cleavage figures it is a small irregula
. The Biological bulletin. Biology; Zoology; Marine biology. MID-BODIES AND CENTRAL BODIES 575 present when the polar bodies are pinched off, but not when the egg divides. Crepidula eggs (ConkHn, 1902) show striking differences in mid- body structure from cycle to cycle. In first polar body figures it is a ring, which appears as two dots when seen in cross-section (Figs. 35 and 36); in the second, it is a smaller ring with a dot in it (Fig. 37), or just a dot (Fig. 38); in first-cleavage figures it is a large area containing a vesicle (Fig. 43); in third-cleavage figures it is a small irregular blob (Fig. 45), and in fourth-cleavage figures, a minute dot (Fig. 46). The difference in size of the mid-bodies is apparently related to the size of the mitotic figures concerned. The factors which produce rings in some cells and vesicles or dots in others are not as yet understood. Variation in the structure of mid-bodies is also exhibited in Enteroxenos cells in different cycles (Figs. 47-57).. Fig. 12. Variation in mid-body structure in Arbacia eggs at first cleavage. Twenty-five bodies selected at random from a single slide are shown in outline and without their accompanying spindle remnants. The unit of the scale is ix. All eggs are in late telophase just after cleavage is completed. Bouin's fixation. Instability of Mid-body Structure Mid-bodies vary in size and shape from cell to cell on the same slide. Outline drawings of mid-bodies in Arbacia eggs at first cleavage (Fig. 12) illustrate the variation in size and contour which may occur in cells at the same stage treated identically and lying side by side on the same slide. The extent of this variation is typical of the materials reported in this paper. Mid-bodies of oogonia (Figs. 47-49) and those of the second polar body figures (Figs. 52-54) in Enteroxenos cells also exhibit variation in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabi
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