DIRECT OR A Mir one 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 Remak's scheme (p. 63). 

 The rapid extension of our knowledge of mitotic division between 

 the years 1875 and 1885 showed, however, that such a mode of 

 division was, to say the least, of rare occurrence, and led to doubts 

 as to whether it ever actually took place as a normal process. As 

 soon, 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 the 



cockroach. [WHEELER.] 



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

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

 ^g^^ in the mole-cricket, where division begins in the fission of the 

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

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

 the nematode RJiabdoucina, by Korschelt in the intestine of the 

 annelid OpJnyotrocha, 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. Ccntrosomc and Attraction-sphere in A mi to sis 



The behaviour of the centrosome in amitosis forms an interesting question 

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

 ('91) that the nucleus of leucocytes might in some cases divide directly without 



