ACHROMATIC FIGURE 197 



the containing cells has occurred. These last two appearances 

 are apparently associated with two different types of fission of the 

 bacterial cell. In the first case, the central structure elongates 

 with the simultaneous elongation of the cell, and later seems 

 to divide by the simple process of pinching through, much as 

 though it had been stretched and had given way in the middle, 

 whereas in the second case, which seems to be derived from the 

 previously described dumb-bell by separation of the two halves, 

 the division of the cells appears to be accomplished by the laying 

 down of a definite transverse wall between the two halves of the 

 central body. 



It would seem a reasonable hypothesis to consider that the 

 various appearances described above represent definite phases in 

 a division cycle (which possibly entails two alternative modes of 

 division of the originally single central body), and that this cycle 

 or cycles is in some way connected with the normal fission process 

 of the bacterial cell (Fig. 73). 



Observations were also made on living cells. These also showed 

 the central body as an ill-defined refractive structure, which in the 

 course of division elongated to a dumb-bell form and finally 

 divided into two halves. Each half passed into one of the daughter 

 cells in the same way as in stained preparations. 



The behaviour of this central body certainly conforms in a 

 remarkable manner to that of a nucleus, and the process of division 

 is apparently typically amitotic in nature. 



ACHROMATIC FIGURE 



Recent investigations on living tissues have introduced a 

 number of modifications into our conception of the origin of the 

 achromatic figure. In plants, unlike animals, it is only in the 

 lower groups that a centrosome is present. This body is absent, 

 for example, in the Spermophyta. Thus, the achromatic figure in 

 plants is of two types, one with asters and centrosome (amphiastral 

 type), and the second without these structures (anastral type). 



In the lower plants, such as the fungi and algae, the achromatic 

 figure is characteristically intranuclear. For a very complete 



