. Cytology, with special reference to the metazoan nucleus. Cells. 9° CYTOLOGY CHAP. Doncaster (1907) for the parthenogenetic eggs of the saw-fly, Nematus ribesii, and later by Schleip (1910) for Rhodites rosae, a gall-fly. A very peculiar phenomenon observed by Brauer (1894) in Artemia also falls into this category. As we have already seen (p. 89), the normal procedure is for only one maturation division to take place, without. Fig. 42. Meiotic prophase in the sexual egg of Branchipus (A-G), and in the parthenogenetic egg of Artemia (H-J). (After Fries, , 1910.) A, young oocyte I. ; B, sy
. Cytology, with special reference to the metazoan nucleus. Cells. 9° CYTOLOGY CHAP. Doncaster (1907) for the parthenogenetic eggs of the saw-fly, Nematus ribesii, and later by Schleip (1910) for Rhodites rosae, a gall-fly. A very peculiar phenomenon observed by Brauer (1894) in Artemia also falls into this category. As we have already seen (p. 89), the normal procedure is for only one maturation division to take place, without. Fig. 42. Meiotic prophase in the sexual egg of Branchipus (A-G), and in the parthenogenetic egg of Artemia (H-J). (After Fries, , 1910.) A, young oocyte I. ; B, synizesis and leptotene stage ; C, zygotene, D, pachytene stages ; E, F, G, contraction of the chromosomes into the definitive bivalents ; H, young oocyte I. ; I, late prophase, chromosomes longitudinally split; J, definitive chromosomes of the maturation division. reduction of chromosome number. As a rare exception, however, Brauer found that a second division took place, again without reduction. The two nuclei resulting from this second mitosis must be regarded as equiva- lent to the nuclei of the mature egg and second polar body. The latter, however, is not extruded from the egg, but remains close to the egg nucleus and moves with it to the centre of the egg. Thereafter these two nuclei act like the male and female gamete nuclei in fertilization,. 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 Agar, W. E. (Wilfred Eade), 1882-1951. London, Macmillan and Co. , limited
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