. The cell in development and inheritance. Cells. THE MECHANISM OF MITOSIS 71 K-ac cz- evidence derived from the study of the Ascaris Qgg, and it was here that Van Beneden first demonstrated the fact, already sus- pected by Flemming, that the daughter-chromosomes move apart to the poles of the spindle, and give rise to the two re- spective daughter-nuclei.^ Van Beneden describes the astral rays, both in Asca7-is and in tunicates, as differentiated into sev- eral groups (Fig. 34). One set, forming the " principal cone," are attached to the chromosomes and form one-half of the spin
. The cell in development and inheritance. Cells. THE MECHANISM OF MITOSIS 71 K-ac cz- evidence derived from the study of the Ascaris Qgg, and it was here that Van Beneden first demonstrated the fact, already sus- pected by Flemming, that the daughter-chromosomes move apart to the poles of the spindle, and give rise to the two re- spective daughter-nuclei.^ Van Beneden describes the astral rays, both in Asca7-is and in tunicates, as differentiated into sev- eral groups (Fig. 34). One set, forming the " principal cone," are attached to the chromosomes and form one-half of the spindle, and, by the contractions of these fibres, the chro- mosomes are passively dragged apart. An oppo- site group, forming the " antipodal cone," extend from the centrosome to the cell-periphery, the base of the cone forming the "polar ; These rays, opposing the action of the principal cones, not only hold the centrosomes in place, but, by their con- tractions, drag them apart, and thus cause an actual divergence of the centres. The remaining astral rays are attached to the cell- periphery and are limited by a sub-equatorial circle. Later observations indi- cate, however, that this arrangement of the astral rays is not of general occurrence, and that the rays often do not reach the periphery, but lose themselves in the general Van Beneden's general hypothesis was accepted in the following year by Boveri {'88, 2), who contributed many important additional 1 '83, p. 544- Fig. 34. — Slightly schematic figures of dividing eggs of Ascaris, illustrating Van Beneden's theory of mitosis. [Van Beneden and Julin.] A. Early anaphase; each chcomosome has divided into two. B. Later anaphase during divergence of the daughter-chromosomes, Antipodal cone of astral rays; cortical zone of the attraction-sphere; i. in- terzonal fibres stretching between the daughter-chromo- somes ; medullary zone of the attraction-sphere; principa
Size: 1150px × 2174px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectcells, bookyear1896
