30 



HISTOLOGY. 



the protoplasm which are the beginning of the central spindle. 

 This central spindle becomes larger the more the centrosomes 

 advance toward the poles (Figs. 5-7 ). 



The nuclear membrane undergoes solution and the chromo- 

 somes arrange themselves in the equatorial plane, giving rise to 

 the mother star (monaster) (Figs. 4, d, 4, e, and 8). When the 

 chromosomes are of the form of the letter U, the lower round 

 part is directed toward the centre and the two arms of the loop 

 approach the periphery of the cell. Looked at from above, the 



FIG. 4. 





/' 



Nuclear division in the epithelial cells of the cornea of the frog's larva. X 1400. 

 (a) Epithelial cell with nucleus at rest, (b) Thick knot of chronuitin threads. 

 (c) Loose knot of chromatin threads, (d) Mother star (monaster) viewed from above. 

 (e) Mother star viewed from the side. (/) Daughter star diastn- . (</ , Anaphasc. 

 Daughter stars are moving toward the poles, (h) The daughter nuclei in the form of 

 loose knots. 



chromosomes so arranged have the appearance of a star (Fig. 

 4,d). 



During this stage of the mother star the centrosomes proceed 

 to the poles of the cell, and the striations or threads of the cen- 

 tral spindle can be divided into three groups : (a) the fibres 

 joining the chromosomes with the centrosomes (mantle fibres), 

 (b) the central spindle fibres extending uninterruptedly from 



