. The cell in development and inheritance. Cells; Cells. 234 so ATE PROBLEMS OF CELL-ORGANIZATION minute central granule or centriole. This discrepancy between Boveri and Van Beneden was cleared up in a measure by Heidenhain's beautiful studies on the asters in leucocytes, and the still more thorough later work of Driiner on the spermatocyte-divisions of the salamander. In leucocytes (Fig. 35) the large persistent aster has at its centre a well-marked radial sphere bounded by a circle of microsomes, as described by Van Beneden, but without division into cortical and medullary zones. The astral
. The cell in development and inheritance. Cells; Cells. 234 so ATE PROBLEMS OF CELL-ORGANIZATION minute central granule or centriole. This discrepancy between Boveri and Van Beneden was cleared up in a measure by Heidenhain's beautiful studies on the asters in leucocytes, and the still more thorough later work of Driiner on the spermatocyte-divisions of the salamander. In leucocytes (Fig. 35) the large persistent aster has at its centre a well-marked radial sphere bounded by a circle of microsomes, as described by Van Beneden, but without division into cortical and medullary zones. The astral rays, however, show indications of other circles of microsomes lying out- side the centrosphere. Driiner found that a whole series of such concentric circles might exist (in the cell shown in Fig. 109 no less than nine), but that the inner- most two are often especially distinct, so as to mark off a cen- trosphere composed of a medul- lary and a cortical zone precisely as described by Van Beneden. These observations show conclu- sively that the centrosphere of the radial type is merely the inner- most portion of the aster, which acquires an apparent boundary through the especial development of a ring of microsomes. And. Fig. loy. — spciiiKitogonium of salaman- der. [Druner.] The nucleus lies below. Above is the enormous aster, the centrosome at its centre, its rays showing indications of nine concentric circles of microsomes. The area within the second circle probably represents the " attrac- tion-sphere " of Van Beneden. thus Van Beneden's original view is confirmed, that not only the aster as a whole, but also the centro- sphere, is but a modified area of the general cytoplasmic thread-work. Heidenhain points out that there are many cases — for instance, the young sperm-aster — in which there is at first no clearly marked central sphere, and the rays proceed outward directly from the centro- some. The sphere, in such cases, seems to arise secondarily through
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectcells, bookyear1896
