THE VITAL PHENOMENA OF THE CELL 



185 



portant portions of the nuclear figure have developed in the 

 polar area. However, on account of the difficulty in staining 

 them, and their minute size and extreme delicacy, these appearances 

 are not easily made out at this stage ; further, .they may be more 

 or less concealed by granules, which collect in the protoplasm in 

 their neighbourhood. According to Flemming and Hermann, two 

 centrosomes may be made out in successful preparations. These 

 are situated very close together, and have probably been formed 

 by the division of an originally single centrosome. Between them 

 the connecting fibrils, which later on develop into the spindle, can 

 be seen. 



Second Stage of Division. 



The second stage may be said to date from the time when the 

 nuclear membrane grows indistinct and dissolves. The nuclear 

 sap then distributes itself evenly throughout the cell body, whilst 

 the nuclear segments come to lie freely in the middle of the pro- 

 toplasm (Fig. 78). The two 

 centrosomes, which are now 

 further apart from one an- 

 other, are situated near 

 them. The spindle increases 

 proportionately in size and 

 distinctness, and is seen to 

 consist of a number of most 

 delicate fibrils, stretching 

 continuously from one cen- 

 trosome to the other, as is 

 clearly shown in Hermann's 

 preparation represented in 

 Fig. 78. The centrosomes of 

 the nuclear figure commence 

 at this stage to exercise an influence upon the surrounding proto- 

 plasm. Around each centrosome as centre, innumerable proto- 

 plasmic fibrils group themselves radially, stretching out principally 

 towards that region where the nuclear segments are situated, and 

 appearing to adhere to their surface. From now on, the spindle 

 commences to increase rapidly in size -until it has attained the 

 dimensions seen in Fig. 79. 



Meanwhile the chromatin figure becomes markedly altered (Fig. 

 79). The nuclear segments have grown considerably shorter and 



FIG. 78. Nucleus of a sperm -mother-cell of 

 Salamandra maculata preparatory to division. 

 The spindle is situated between the two centro- 

 somes. (After Hermann (VI. 29), PL 31, Pig. 7.) 



