THE VITAL PHENOMENA OF THE CELL 181 



plasm which is directly in contact with the membrane. At this 

 period they are close to one another, and are in the form of two 

 extremely small spherules. They are composed of a substance 

 which is only stained with difficulty, and which is, perhaps, de- 

 rived from the substance of the nucleolus. These spherules are 

 the pole or central corpuscles (corpuscules, poles, centrosomes), 

 which have been already described. Gradually they separate 

 from one another, describing a semicircle round the upper sur- 

 face of the nucleus, until they take ap their position at opposite 

 ends of the nuclear diameter. 



The nuclear spindle develops itself between the centrosomes. 

 It consists of a large number of very delicate fibrils, which are 

 parallel to one another, and which are probably derived from the 

 linin framework of the resting nucleus. These fibrils diverge 

 somewhat at their centres, and converge at their ends towards the 

 centrosomes, in consequence of which the bundle assumes more 

 or less the shape of a spindle. At first, when the centrosomes 

 are just commencing to separate, the spindle is so small, that it 

 can only be made out with difficulty, as a band connecting them 

 together. However, as the centrosomes separate from one 

 another, the spindle increases in size, and becomes more clearly 

 defined. 



The protoplasm also commences to arrange itself around the 

 poles of this nuclear figure as though attracted by them. Thus 

 an appearance, similar to that seen at the ends of a magnet, 

 which has been dipped in iron filings, is produced. The proto- 

 plasm forms itself into a large number of delicate fibrils, which 

 group themselves radially around the centrosome as a middle 

 point or centre of attraction. At first they are short and confined 

 to the immediate neighbourhood of the attraction centre. How- 

 ever, during the course of the process of division they increase in 

 length, until finally they extend throughout the whole length of 

 the cell. This arrangement of the protoplasm around the pole is 

 variously described as the plasmic radiation, radiated figure, star, 

 sun, etc., in consequence of its resemblance to the rays of light, 

 attraction spheres, etc. 



These are briefly the various elements out of which the nuclear 

 division figures are built up. The centrosomes, the spindle, 

 and the two plasmic radiations have been grouped together by 

 Flemming under the name of the achromatin portion of the dividing 

 nuclear figure, in contradistinction to the various appearances 



