CELL MULTIPLICATION 



89 



several nuclei. In most instances the division of the cell is 

 simply delayed and takes place later, so that finally the con- 

 dition of a single nucleus in each cell is resumed. This occurs 

 in the dividing egg of insects, for example. In some instances, 

 however, the cell body does not divide at all, and the continued 

 division of the nucleus produces a connected mass of proto- 

 plasm with many nuclei. This occurs, for example, in some 

 molds shown in Figure 42 E, in which there is no sign of cell 

 division, although there are many nuclei. Such a condition 

 is called a syncytium (Gr. syn = together + cytos = cell) and 

 is sometimes described as acellular. This multicellular state 

 with incompleted cell division is rare, for in most instances 

 the division is completed promptly. 



Amitosis. While division by karyokinesis is the common 

 method of cell division among all organisms, there are some 

 instances where cells divide without 

 going through these stages. This is 

 most likely to occur in the old age of 

 the cell when its vitality begins to de- 

 cline. In these cases, the nucleus di- 

 vides directly ; sometimes being simply 

 pinched into two parts (Fig. 37), some- 

 times being compressed into a middle 

 plate which divides into two halves 

 and then separates, and sometimes 

 forming two nuclear membranes in- 

 side of the original membrane which 

 then ruptures and permits the escape 

 of the new nuclei. In these cases, 

 it frequently happens that, though 

 the nucleus divides, the cell body 

 does not divide, so that 'there re- 

 sults a cell with more than one nucleus. This process of di- 

 vision is called amitosis (Gr. a = without + Lat. mitos = thread), 

 and it is thought to indicate a decline in the vigor of the cells. 



d 



FIG. 37. DIAGRAM SHOW- 

 ING THE PROCESS OP 

 NUCLEAR DIVISION BY 

 AMITOSIS 

 (Modified from Wheeler.) 



