. Cytology, with special reference to the metazoan nucleus. Cells. CHAP. IV THE SEX CHROMOSOMES 99 term of Sex Chromosomes is, however, a sufficient and obvious description of them, and by this name they will be called here. Owing to the comparative ease and certainty of the observations, and to the interest due to their relation to sex, a great mass of knowledge of these sex chromo- somes has been accumulated in recent years, American cytologists having been particularly active along these Fig. 45. The chromosomes of Protenor belfragei. (A, I-K, from Morrill, , 1910; R-E, H, after
. Cytology, with special reference to the metazoan nucleus. Cells. CHAP. IV THE SEX CHROMOSOMES 99 term of Sex Chromosomes is, however, a sufficient and obvious description of them, and by this name they will be called here. Owing to the comparative ease and certainty of the observations, and to the interest due to their relation to sex, a great mass of knowledge of these sex chromo- somes has been accumulated in recent years, American cytologists having been particularly active along these Fig. 45. The chromosomes of Protenor belfragei. (A, I-K, from Morrill, , 1910; R-E, H, after Montgomery, Tran$. Amer. Phil. Soc, 1901 ; F, G, from Wilson, , 1906.) A, spermatogonial metaphase group. Twelve ordinary and one sex chromosome. B, prophase I., i ; C, metaphase I., (J ; D, anaphase I., ^ ; E, early anaphase II. in the (J. Sex chromosome passing ui divided to one pole. F, G, polar views of the chromosome groups at each pole of the spindle in anaphase II. One group with the sex chromosome, the other without. H, late anaphase II., showing one spermatid with the sex chromosome, the other without I, oogonial metaphase group, twelve ordinary and two sex chromosomes ; J, chromosome group from 3 male embryo ; K, chromosome group from a female embryo. X, the sex chromosome. As a typical example of an animal with sexual dimorphism of chromosomes we may take the Hemipteran insect Protenor helfra^ci (Fig. 45). Its chromosome cycle has been worked out by Montgomery (1901 h), Wilson (1906 h, etc.) and Morrill (1910). The spermatogonial chromosome groups (A) show thirteen chromo- somes, one being more than twice as large as any of the others. This. 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
