The cell in development and inheritance . mains in the resting state (reticulum), and there is no formationof a spireme or of chromosomes. Second, division occurs withoutthe formation of an amphiaster; hence the centrosome is not con-cerned with the nuclear division, which takes place by a simpleconstriction. The nuclear substance, accordingly, undergoes a divi- ^ 93. PP- 203, 204. 2 ic, p. 205. DIRECT OR AMITOTIC DIVISION 115 sion of its total mass, but not of its individual elements or chromatin-granules (Fig. 56). Before the discovery of mitosis, nuclear division was generally-assumed to ta
The cell in development and inheritance . mains in the resting state (reticulum), and there is no formationof a spireme or of chromosomes. Second, division occurs withoutthe formation of an amphiaster; hence the centrosome is not con-cerned with the nuclear division, which takes place by a simpleconstriction. The nuclear substance, accordingly, undergoes a divi- ^ 93. PP- 203, 204. 2 ic, p. 205. DIRECT OR AMITOTIC DIVISION 115 sion of its total mass, but not of its individual elements or chromatin-granules (Fig. 56). Before the discovery of mitosis, nuclear division was generally-assumed to take place in accordance with Remaks scheme (p. 63).The rapid extension of our knowledge of mitotic division betweenthe years 1875 and 1885 showed, however, that such a mode ofdivision was, to say the least, of rare occurrence, and led to doubtsas to whether it ever actually took place as a normal process. Assoon, however, as attention was especially directed to the subject,many cases of amitotic division were accurately determined, though. Fig. 56.— Group of cells with amitotically dividing nuclei; ovarian follicular epithelium of thecockroach. [Wheeler.] very few of them conformed precisely to Remaks scheme. Onesuch case is that described by Carnoy in the follicle-cells of theQgg in the mole-cricket, where division begins in the fission of thenucleolus, followed by that of the nucleus. Similar cases havebeen since described, by Hoyer(90)in the intestinal epithelium ofthe nematode Rhabdonema, by Korschelt in the intestine of theannelid Ophryotrocha, and in a few other cases. In many cases, how-ever, no preliminary fission of the nucleolus occurs; and Remaksscheme must, therefore, be regarded as one of the rarest forms ofcell-division (!). 2. Centrosomc and Attraction-spJicrc in Auiitosis The behaviour of the centrosome in aniitosis forms an interesting questionon account of its bearing on the mechanics of cell-division. Flemming obser\edC91) that the nucleus of leucocytes migh
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1902
