. The Biological bulletin. Biology; Zoology; Marine biology. 244 MARY BLOUNT. the blastoderm at 4:25 P. M., or twenty and a half hours after fertilization. Some of these cells at least have been derived by division of such a marginal blastomere as shown in Fig. 9. Others may have been derived from the periblast, with nuclei sisters to those yet remaining in the unsegmented part. Fig. 11 is the posterior end of a longitudinal section through an egg perhaps twenty-five hours after fertilization (8:50 P. M.) Four nuclear nests and two single nuclei are found in the peri- blast. Beyond the limits
. The Biological bulletin. Biology; Zoology; Marine biology. 244 MARY BLOUNT. the blastoderm at 4:25 P. M., or twenty and a half hours after fertilization. Some of these cells at least have been derived by division of such a marginal blastomere as shown in Fig. 9. Others may have been derived from the periblast, with nuclei sisters to those yet remaining in the unsegmented part. Fig. 11 is the posterior end of a longitudinal section through an egg perhaps twenty-five hours after fertilization (8:50 P. M.) Four nuclear nests and two single nuclei are found in the peri- blast. Beyond the limits of the drawing, are four other nuclei. Fig. 11. Posterior side of a longitudinal section of a pigeon's egg about twenty- five hours after fertilization, 8:50 P. M. I. Nests of periblast nuclei. 2. Periblast nucleus. 3. Syncytial mass derived from the periblast, organizing into cells which will be added to the blastodisc. 4. Vacuoles. two of them are in line with the most extreme nucleus to the left and two are a little deeper. Large masses, as shown at 3, Fig. 11, are organized out of the periblast and subsequently they divide into smaller cells. Indentations just to the left of the segmented part here suggest future cleavage which would add superficial cells. (Compare Fig. 14.) This figure (Fig. 11) re- sembles Harper's (3) Fig. 36 which is a section of an egg fifteen hours after fertilization. Harper considers that the " free nuclei " are sperm nuclei but there was a gap in his material just at the period when the sperm nuclei disappear and the periblast is organized. The nuclei of his Fig. 36 are doubtless periblast nuclei. Fig. 12 shows a marginal part of a horizontal section through an egg of the same age as Fig. 11 (twenty-five hours after fertili- zation, 8:50 P. M.). Here are "free nuclei" or periblast nu-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appea
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