DIRECT OR A MIT OTIC DIVISION 



81 



many cases of amitotic division were accurately determined, though 

 very few of them conformed precisely to Remak's scheme. One 

 such case is that described by Carnoy in the follicle-cells of the 

 egg in the mole-cricket, where division begins in the fission of the 

 nucleolus, followed by that of the nucleus. Similar cases have 



Fig. 40. Group of cells with amitotically dividing nuclei ; ovarian follicular epithelium of 

 the cockroach. [WHEELER.] 



been since described, by Hoyer ('90) in the intestinal epithelium of 

 the nematode Rhabdonema, by Korschelt in the intestine of the 

 annelid Ophryotrocha, and in a few other cases. In many cases, how- 

 ever, no preliminary fission of the nucleolus occurs; and Remak's 

 scheme must, therefore, be regarded as one of the rarest forms of 

 cell-division ( ! ). 



2. Centrosome and Attraction-Sphere in Amitosis 



The behaviour of the centrosome in amitosis forms an interesting question 

 on account of its bearing on the mechanics of cell-division. Flemming ob- 

 served ('91) that the nucleus of leucocytes might in some cases divide directly 

 without the formation of an amphiaster, the attraction-sphere remaining undivided 

 meanwhile. Heidenhain showed in the following year, however, that in some 

 cases leucocytes containing two nuclei (doubtless formed by amitotic division) 

 might also contain two asters connected by a spindle. Both Heidenhain and 

 Flemming drew from this the conclusion that direct division of the nucleus is in 

 this case independent of the centrosome, but that the latter might be concerned in 

 the division of the cell-body, though no such process was observed. A little later, 

 however, Meves published remarkable observations that seem to indicate a functional 

 activity of the attraction-sphere during amitotic nuclear division in the "sperma- 



