MUSEUM OF COMPARATIVE ZOOLOGY. 525 



no representation of them in his figures, and says in the text (p. 24) that 

 these conelike nuclei of the yolk exert no influence on the surrounding 

 protoplasm. It is perhaps impossible to draw a conclusion of universal 

 applicability from these accounts, but it will be granted that it is pos- 

 sible for stellate figures to accompany the division of nuclei in syncytia, 

 as well as in definitely limited cells. The existence of asters in syncytia 

 once established, it still remains to be ascertained whether they will cast 

 any light on the supposed share which the nucleus takes in their pro- 

 duction, or on the nature of the influence they exert upon the nucleus 

 during its division. For the present I see no reason to anticipate the 

 -necessity of modifying the views I have arrived at from a study of cell 

 nuclei. 



Plant cells rarely aflbrd the opportunity of studying the radial phe- 

 nomena in the protoplasm during nuclear division, as Strasburger and 

 others have already pointed out. Why the centres of attraction exert 

 apparently so little influence on the protoplasm, it is difficult to say. 

 The great size of the nucleus as compared with the mass of the cell pro- 

 toplasm, and the vacuolation of the latter, are features which restrict 

 the possibility of well-marked asters. Certain it is that they are not so 

 clearly defined as in animal cells, though there are evidences of a radial 

 tendency in the protoplasmic filaments of Spirogyra, etc. The poles of 

 the spindle are usually so near the surface of the protoplasm that there 

 is little opportunity to form extensive rays. Cases where the centres of 

 attraction lie wholly outside the nuclear structure in plants (Isoetes) are 

 not numerous, but I cannot think such unfavorable objects as plant cells 

 and animal tissue-cells are competent to cast doubt on the nature of what 

 is so evident in the segmentation of eggs. Strasburger gives assurance 

 that in division the nucleus first becomes homogeneous, and then a con- 

 trast is developed between two opposing points of its surface. The latter 

 are doubtless equivalent to the astral centres, and the difference in the 

 order of events as compared with Limax may possibly be explained as 

 resulting from the inconspicuous nature of the asters in plant cells, 

 whereby their earliest stages have been overlooked. 



In what precedes I have endeavored to show the possibility of a much 

 earlier origin for the asters than has generally been recognized, — that 

 they precede the disintegration of the nucleus, and are therefore to be 

 looked upon, not as the result of a segregation already effected in the 

 nuclear substance, but as the seat of forces actively engaged in remod- 

 elling the constituents of this central body. So long as it remained 

 undisputed that the centres of the asters lay within the nucleus, or at 



