56 Papers from the Marine Biological Laboratory at Tortugas. 



instances where the chromosomes thus related to the nucleolus do stiil pass 

 into and help complete the first maturation spindle. The point of impor- 

 tance seems to be that some connection, however remote, be established 

 whereby chromatin may be transferred from the nucleolus to the chromo- 

 somes. Such cross-connections of chromatin are very frequent and conspic- 

 uous. There remains little doubt that the arrangement signifies a transfer 

 of matter from the nucleolus to the chromosomes. Moreover, the chromo- 

 somes, in cases where such connections are made, always increase in size 

 before they pass to the spindle. Where the chromosomes are in such inti- 

 mate relation with the nucleolus that they detach themselves from it at 

 maturation (figs. 51, 52, 58, 59) they are frequently seen to draw cut the 

 chromatin after them, thus giving the appearance of coming from out of 

 the nucleolus (figs. 52, 54) . The entire body of the nucleolus is broken up 

 at this time, and each particle, with its plastin ground-substance and some 

 of the fragments, is drawn toward the spindle, only, however, to contribute 

 their substance to the growing chromosomes or to be eventually resorbed 

 by the cytoplasm. What chromatin is not thus disposed of for the time 

 being may be retained as a small spherical nucleolus lying in the residual 

 substance of the nucleus until about the time that the second polar spindle is 

 formed (fig. 60). It seems important to emphasize again that in Asterias 

 forbesii the chromosomes are not derived from out of the nucleolus, but 

 that a close connection is generally established between the two, for the 

 purpose of bringing about a transfer of chromatin material, the chromo- 

 somes in consequence increasing in size during the early maturation stage. 



THE POLAR SPINDLE AND POLAR BODIES. 



After an interval of from 30 to 45 minutes the first polar spindle is 

 formed. The transfer of the chromosomes from the nucleus to the com- 

 plete spindle is effected in from 20 to 30 minutes. The process appears to 

 be as follows : While the asters are still close together their rays have pene- 

 trated into the nucleus and some of these (Zugfasern) have become attached 

 to the chromosomes. Which is the active factor in effecting a connection I 

 have been unable to determine. It seems likely, however, that the astral rays 

 seek the chromosomes (largely a fortuitous matter, except that the two are 

 normally always in the same vicinity of the nucleus) rather than the reverse. 

 As the chromosomes are becoming attached to the rays, the asters gradually 

 move apart, progressively decreasing the angle at which the rays spring 

 from the centrospheres and so drawing the chromosomes into the spindle, 

 whose rays are now approximately horizontal to the periphery of the egg 

 and parallel to each other. The astral rays become arranged parallel to each 

 other and continuous from one centrosphere to the other by blending of those 

 from separate asters to form the central spindle. Some of the spindle 

 fibers are clearly stouter than others, and it seems very probable that here 



