Archive image from page 74 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar Year: 1920 II MEIOSIS IN THE FEMALE 59 The particular problems raised by the germinal vesicle stage in oogenesis are : (i) The continuity of the chromosomes throughout this period. (2) The relation between the chromosomes and the nucleoli. (3) The connection between the pecuhar germinal vesicle stage and the synchronous enormous growth of the cytoplasm of the egg, together with the formation of yolk. (4) Does any comparable stage occur in spermatog
Archive image from page 74 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar Year: 1920 II MEIOSIS IN THE FEMALE 59 The particular problems raised by the germinal vesicle stage in oogenesis are : (i) The continuity of the chromosomes throughout this period. (2) The relation between the chromosomes and the nucleoli. (3) The connection between the pecuhar germinal vesicle stage and the synchronous enormous growth of the cytoplasm of the egg, together with the formation of yolk. (4) Does any comparable stage occur in spermatogenesis ? (i) The Continuity of the Chromosomes The conditions in the germinal vesicle have been urged against the theory of the genetic continuity of the chromosomes, since in some species the fully developed germinal vesicle—which it must be remembered is interposed between syndesis and metaphase I.—shows no trace of Fig. 23. A chromosome from the germinal vesicle of Prisiiurus. (After Ruckert. , 1892.) chromosomes. This condition occurs, for instance, in many Echinoder- mata, whose fully developed germinal vesicle consists of an enormous nucleolus suspended in a fine, very faintly staining, reticulum in which no trace of individual chromosomes can be detected. As in the case of the resting stage between two ordinary somatic mitoses, however, we must ascribe the invisibiUty of the chromosomes in such germinal vesicles to their extreme diffusion and loss of staining power, and not to any loss of identity. This can be clearly determined by a comparative study of this period of oogenesis. In the Copepoda (a group which has been extensively studied in this connection) we find a great range of variation in the degree of certainty with which the chromosomes can be recognized throughout the growth period ( Matschek, 1910). In Cyclops gracilis the chromosomes remain sharply individuahzed throughout, as is also the case in Hcicrocope salicns (Fig. 24). In Diaptomus casto
Size: 2206px × 907px
Photo credit: © Actep Burstov / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: 1920, agar_wilfred_eade_1882_, archive, book, bookauthor, bookdecade, bookpublisher, booksponsor, booksubject, bookyear, cells, drawing, historical, history, illustration, image, london_macmillan, ncsu_libraries, page, picture, print, reference, vintage, zimmermann_a_albrecht_b_1860
