. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. 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. (â 3) The connection between the peculiar 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 v
. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. 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. (â 3) The connection between the peculiar 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 vesicleâwhich it must be remembered is interposed between syndesis and metaphase I.âshows no trace of. Fig. 23. A chromosome from the germinal vesicle of Pristiurus. (After Riickert. , 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 invisibility 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 individualized throughout, as is also the case in Hetcrocope saliens (Fig. 24). In Diaptonms castor, however (Fig. 25), the chromosomes become very diffuse at the height of the
Size: 2467px × 1013px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectcells, bookyear1920
