. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. ib'. // S^ 1l M of chromidia formation —is supposed to be of frequent occurrence. The three forms, Mas- tigella, Coccidium and Arcella will serve as examples. During the asexual multiplication of Mas- tigella viirea (Gold- schmidt, 1907) the nuc- leus divides by mitosis with well - developed chromosome formation. In gametogenesis, how- ever, the gamete nuclei are produced from the nucleus of the gameto- cyte by a very different process (Fig. 87). There is a copious emission of chromidia from the nucleus into the cyto-
. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. ib'. // S^ 1l M of chromidia formation —is supposed to be of frequent occurrence. The three forms, Mas- tigella, Coccidium and Arcella will serve as examples. During the asexual multiplication of Mas- tigella viirea (Gold- schmidt, 1907) the nuc- leus divides by mitosis with well - developed chromosome formation. In gametogenesis, how- ever, the gamete nuclei are produced from the nucleus of the gameto- cyte by a very different process (Fig. 87). There is a copious emission of chromidia from the nucleus into the cyto- plasm. In the mass of chromidia numerous nuclei (up to two or three hundred) are formed by aggregation of numbers of chromidia into clumps. The nuclei thus formed then (in the case of the macrogamete) divide by mitosis (with chromosome formation) at least once. Gold- schmidt interprets this as a reduction division, as it results in only one of the two daughter groups of chromosomes forming a functional nucleus, the other degenerating into a body strikingly reminiscent of the Metazoan polar body. The micro- and macrogametes unite in syngamy, the zygote nucleus dividing by mitosis to introduce the asexual cycle with which we began. The chroiiiosoincs of Aggregata eberthi. They are designated a-f, from the largest (a) to the smallest (/). (Dobell and Jameson, , igi5.) A microgametocytc nucleus in prophase, with six chromosomes ; B, equatorial plate, and C, anaphase of same ; D, zygote nucleus in pro- phase for its first division: E, equatorial plate of same division—homo- logous chromosomes united into bivalents; F, anaphase of same (reduction division).. 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, Wilfred Eade, 1882-. London Macmillan
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectcells, bookyear1920
