INDIRECT DIVISION. 37 



segmentation of the spirem, the centrosome has divided into 

 two, which have separated and become located at opposite 

 points or poles, one on each side of the nucleus. 



In the equatorial or aster stage the process is at its height. 

 The achromatic spindle has developed, consisting of delicate 

 striae, uncolored by the stain (whence the term achromatic), 

 which are arranged in the form of two cones having their 

 apices in the two centrosomes, and their bases directed toward 

 each other ; or, in other words, the achromatin-fibres form a 

 fusiform spindle, with the extremities in the centrosomes or 

 poles (Fig. 9). The chromosomes become arranged in the 

 equatorial plane of this spindle that is, in the plane bisect- 

 ing at right angles the axis or line connecting the two poles ; 

 their loops are directed inward toward the common centre; 

 their arms and free extremities extend outward in a radiating 

 manner, presenting the appearance, from the side, of a star, 

 or aster. 



The next stage is the division of the chromosomes and migra- 

 tion of their segments, or metakinesis. The chromosome-fila- 

 ments split in two longitudinally, beginning at the apex or 

 bend, and the apices of the separated halves then travel along 

 the threads of the achromatic spindle toward the two cen- 

 trosomes. 



Thus the double aster or diaster stage develops. Around 

 each centrosome the daughter-chromosomes become arranged 

 in radiating or the aster form. The chromatin of the single 

 original nucleus has been divided into two equal parts, to 

 form two new da lighter- nuclei ; and it is to be observed that 

 the number of chromosomes in the daughter-cells is precisely 

 the same as in the parent-cell, and remains constant through- 

 out for each species. 



The free ends of the chromosome-fibers become connected 

 by achromatic filaments, and the chromatin-fibers now undergo 

 a change precisely the reverse of that of developing karyo- 

 kinesis. The double segmented convolution, or disconnected 

 chromosomes, is succeeded by the double continuous convolu- 

 tion: first the open skein appearing, then the close skein. 

 The nuclear membrane and nucleoli appear, and ultimately 

 the nuclei resume the condition of the resting stage. Simul- 

 taneous with these retrograde processes in the nuclei, division 



