456 WILSON. [Vol. XI. 



in some degree comparable to the progressive rearrangement 

 of iron-filings in a moving magnetic field but differing in the 

 fact that the aster grows as it moves and thus extends its 

 sphere of action (whence the growth of the astral rays). 



The term "archoplasm " has accordingly no significance save 

 in a topographical sense ; it is that portion of the general 

 thread-work that is for the time being differentiated into astral 

 rays and spindle-fibres, and in view of the misleading etymology 

 of the word, it may well be dropped from the cytological vocabu- 

 lary as Heidenhain has already suggested.^ 



II. The Chromatin. 



The history of the chromatin will be very briefly considered, 

 since my main purpose is to indicate its probable relation to 

 the linin network and to the spindle-fibres. As stated at p. 

 450 the sperm-nucleus and egg-nucleus completely fuse to form 

 a cleavage-nucleus. During the ensuing "pause" this nucleus 

 greatly increases in size, so that its bulk may finally become 

 four to six times that of the original egg-nucleus (in Arbacia as 

 Mathews has shown, the growth at this period is still greater). 

 This growth is not due merely to a swelling of the nucleus, but 

 involves a large increase in the amount of chromatin. Through- 

 out the growth-period the chromatin forms an irregular and 

 discontinuous network, the threads of which consist of rounded 

 granules arranged in irregular strings or cords. Besides these, 

 however, the nucleus almost always contains a number of 

 separate chromatic rings, variable in number and size, which 

 stain precisely like the network. Close examination shows 

 that the chromatin-granules are suspended in the meshes of an 

 achromatic network (linin) the threads of which here and there 

 are free from chromatin and thus come clearly into view. The 

 linin is, however, small in amount and hard to see until a little 

 later. 



A. Prophases. — At the close of the pause, when the nucleus 

 has attained its maximum size and is preparing for division, its 

 substance undergoes a very rapid and remarkable transforma- 



1 Kern und Protoplasma, p. 154. 1892. 



