268 



WATASE. 



[Vol. IV. 



The question naturally arises, How is this separation of a 

 single "plate" into two "plates" effected? With the separa- 

 tion of the two daughter "plates " of chromosomes, there comes 

 into existence a series of parallel interzonal filaments which lie 

 between the two separating " plates." The separation of the 

 daughter "plates" of chromosomes, and the formation of the 

 interzonal filaments, are so intimately connected with one 

 another that we naturally look for a causal connection which 



underlies the parallel se- 

 ries of phenomena. Any 

 theory which explains the 

 one must also explain the 

 other. 



Before I venture a sug- 

 gestion in regard to this 

 important point, it will 

 be important to find out 

 whether the phenomenon 

 of polar flattening of the 

 nucleus, such as I have 

 described in the previous 

 pages, is one of normal 

 character or not. That the 

 said phenomenon is of a 

 normal character is shown 

 by its constant occurrence 

 in the blastoderm of the 

 squid, where all the differ- 



A— r 



Figure IX. 



ent stages of caryokinetic division can be observed without 

 any difficulty. My recent studies on the eggs of a starfish {Aste- 

 rias vulgaris), with this particular point in mind, convinced me 

 that there, as in the squid, the polar invasion of the nucleus by 

 the archoplasmic filaments is the matter of normal occurrence. 

 This phase, however, is extremely transient, and quickly passes 

 into the equatorial plate stage. 



In connection with the caryokinetic phenomena in Pagiirns 

 striates, Carnoy ^ observed the formation of the equatorial chro- 

 matic plate by the " gradual retraction of the chromatic loops 



^ Carnoy: Cytodierese chez les Arthropodes, PI. VII, Fig. 44, a, b, c, d,f, p. 316. 



