Archive image from page 201 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar_0 Year: 1920 i86 CYTOLOGY CHAP. In the following three cases the meiotic disturbance must be ascribed to physiological causes, since the degenerative changes that take place in the nucleus are more profound, even though in some cases the number of chromosomes in the parent species is the same. Matings between the magpie pigeon (6) and dove ( ? ) (Smith, 1913) result in male offspring only. These are found to exhibit a meiosis differing from the n
Archive image from page 201 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar_0 Year: 1920 i86 CYTOLOGY CHAP. In the following three cases the meiotic disturbance must be ascribed to physiological causes, since the degenerative changes that take place in the nucleus are more profound, even though in some cases the number of chromosomes in the parent species is the same. Matings between the magpie pigeon (6) and dove ( ? ) (Smith, 1913) result in male offspring only. These are found to exhibit a meiosis differing from the normal in that there is an irregular metaphase I. and, doubtless in consequence of this, the second meiotic division appears to be omitted. In any case it was never found, though spermatogenesis proceeds without it, resulting in the formation of spermatozoa, 77 per cent of which are about twice the size of those of either parent. The The chromosomes ol certain Lepidoptera and their hybrids. (After Harrison and Doncaster, , 1914.) All are polar views of equatorial plates. A, B, Lycia hirtaria. A, oogonium showing 28 chromosomes ; B, spermatocyte I., 13 bivalents (one compound). C, D, Ithysiazonaria. C, spermatogonium, about 112 chromo- somes ; D, spermatocyte I., 56 bivalents. E, F, the hybrid, /.zonariaxL. hirtaria. E, spermatogonium, 14large (hirtaria), and about 56 small (zonaria) chromosomes; F, spermatocyte I., 63 chromosomes. G, spermato- cyte I. of the reciprocal hybrid, about 60 chromosomes, showing the two parental types. experiments indicate that the spermatozoa are not functional, for two of the hybrid males were paired with female pigeons, which laid and incubated eggs which, however, proved unfertile. In the hybrids between different species of pheasant (Smith and Thomas, 1913), and pheasant and domestic fowl (Cutler, 1918), no normal stages can be observed after synizesis. These hybrids are of course sterile. When they are females the resulting anatomical abnorm
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