SOIL PROTOZOA. 323 



In the equatorial ring of chromatin granules I have not been 

 able to distinguish at all clearly the separate constituent chromo*- 

 somes. This may be due to the fact that they become very 

 closely packed together. They are most distinctly seen in 

 figs. 53 &, 54. The equatorial ring becomes divided into two in 

 the plane at right angles to the axis of the spindle. I have not 

 discovered any organism showing the actual constriction of the- 

 chromosomes, but have obtained a stage where the two daughter- 

 rings are very closely apposed (tig. 56). In the succeeding stages, 

 of division the two rings of chromatin gradually become sepa- 

 rated from each other by a wider interval, owing to the elonga- 

 tion of the spindle, the fibres of which become quite distinct 

 across the centre of the animal. 



The poles of the spindle remain sharply pointed until a late 

 stage in the separation of the new chromatin bands (figs. 59 & 60). 



After the stage which is depicted in fig. 55, the word " band " 

 more accui-ately desciibes the appearance presented by the 

 daughter chromatin elements, for I have not been able to make 

 out any ring-like structure after carefully focussing on these 

 parts. Neither have I been able to distinguish separate chromo- 

 somes, for each band appears to be composed of numei-ous fine 

 granules. The nuclear membrane appears to remain intact up 

 to the stage shown in fig. 56, after which, however, it is not dis- 

 tinguishable, and I suppose it disappears entirely. 



The animal now elongates in the direction of the long axis of 

 the spindle and becomes ellipsoidal in outline (fig. 59). This 

 figure shows an interesting condition of the spindle-fibres be- 

 tween the chromatin bands, in that a twist in them seems to 

 have been produced as though one of the bands had rotated 

 through an angle of 180°. A constriction now appears round 

 the animal, and the first stage in the process of fission is brought 

 about. Fig. 60 represents this stage, and it is easily seen that 

 the poles of the spindle are sharply pointed at this time. 



The process of the re-formation of the daughter-nuclei now 

 begins. The pointed poles of the spindle disappear, and the 

 chromatin granules become scattered ii-regularly in a mass of 

 faintly staining linin particles which are apparently formed by 

 the break-up of the outer portion of the spindle-fibres. In 

 fig. 61 one daughter-nucleus is seen to consist of a crescentic 

 area of linin particles in Avhich the small granules of chromatin 

 are scattered, whilst at the other end of the spindle the daughter- 

 nucleus consists of a small though well-developed central granule, 

 no doubt formed by a fusion of smaller granules, surrounded by 

 a ring of linin particles, from which it is separated by a clear 

 zone. I think there can be no doubt that the crescentic daughter- 

 nucleus represents an earlier stage in the process of reorganisa- 

 tion than the round form in the other part of the constricted 

 amoeba. 



In fig. 62 the constriction of the parent amoeba has been 

 carried a little further, and the spindle-fibres between the 



