. The development of the albino rat, Mus norvegicus albinus. Embryology -- Mammals; Rats. DEVELOPMENT OF THE ALBINO RAT 15 The stage of pronuclei was observed in over 100 ova of the white rat by Sobotta and Burckhard. According to these c)b- servers, the two pronuclei show in the earUer stages of tlicir development, large chromatin-like nucleoH, the number of which varies. Some little time later, one or several such chroma- toid nucleolar bodies with irregularly formed chromatin masses arranged on the linin network are to be observed. At a still later time, the chromatin becomes distributed ov
. The development of the albino rat, Mus norvegicus albinus. Embryology -- Mammals; Rats. DEVELOPMENT OF THE ALBINO RAT 15 The stage of pronuclei was observed in over 100 ova of the white rat by Sobotta and Burckhard. According to these c)b- servers, the two pronuclei show in the earUer stages of tlicir development, large chromatin-like nucleoH, the number of which varies. Some little time later, one or several such chroma- toid nucleolar bodies with irregularly formed chromatin masses arranged on the linin network are to be observed. At a still later time, the chromatin becomes distributed over the linin network, throughout the nuclear space, giving the appearance of a fine chronxatin network. One of the pronuclei is, as a rule, somewhat smaller than the other. This is regarded as the male. Fig. 1 Tubal ova, albino rat. X 200. A, rat No. 110, 24 hours, 15 min., ovum in pronuclear stage, larger nucleus female pronucleus; B, and C, rat No. 59, 2 days, 2-cell stages, thin oolemma showing in C, only partially seen in B; D, rat No. 62, 2 days, 22 hours, 3-cell stage, the nucleus of the unsegmented blastomere in the monaster phase, only one of the other two cells showing in the figure. pronucleus, since near it the 'sperm centrum' was now and then observed. The pronuclei lie in about the center of the ovum. The pronuclear stages of my own material, observed in 34 ova, obtained 24 hours after the beginning of insemination— thus at the end of the first day of development—all present essen- tially the same stage of metamorphosis. As may be seen in .\ of figm-e 1, the nuclei are distinctly membraned, and are of relatively large size. The ovum here sketched measures in the stained preparation 70 /x by 62 ix, and is, therefore, of slightly oval form. Sobotta and Burckhard give 55 m to 60 m as the size of the tubal ova, and 60 ^ to 65 m as the size of the ovarian ova in. Please note that these images are extracted from scanned page images that may have been digitally enhanc
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