No. 3.] STL/D/ES ON CEPHALOPODS. 275 



tous bodies in the intermediate zone, which fact has already been 

 pointed out by several investigators. 



Observing, then, (i) that the interzonal portion of the caryo- 

 kinetic figure consists of the bundle of filamentous substance, 

 (2) that this filamentous substance is essentially the same as 

 the archoplasmic filaments of the spindle, (3) that the length of 

 these filaments is exactly the same as the space between the 

 parallel bands of chromosomes in all stages, (4) that the archo- 

 plasmic filaments have been growing in length from the poles 

 toward the equator of the nucleus, and (5) that the interzonal 

 filaments came into existence exactly at the moment when the 

 single equatorial " plate " was dividing into two parallel daughter 

 "plates," the following view becomes probable, viz. that after 

 the archoplasmic filaments from the two centres have reduced 

 the chromatic contents of the nucleus into a flat " plate " by 

 gradual lengthening, they continue to grow in the same manner, 

 and push through between each other, just as two brushes 

 would do if their ends were pushed together. Their free 

 ends dovetail with each other. The distal extremity of each 

 archoplasmic filament being fastened to the chromosome, the 

 latter will be carried by the former at its tip, and will be pushed 

 forward as long as the filament continues to grow. Two op- 

 posing systems of the archoplasmic filaments behaving in a 

 similar way, and lengthening in a contrary direction, would 

 reduce the spherical nucleus first to a biconcave disc, then to 

 a flat "plate," and finally, into two parallel "plates," each 

 "plate" travelhng in an opposite direction. The interzonal 

 filaments then, according to this view, are the actual continua- 

 tions of the archoplasmic filaments ; but, instead of consisting 

 of a single system, as at either end of the spindle, they are 

 composed of two systems, each dovetailing with the other, and 

 growing in contrary directions. Interzonal filaments are, there- 

 fore, the prolongations of the intranuclear filaments. I am 

 further inclined to believe that a certain optical peculiarity of 

 the interzonal region, as, for instance, its aversion to take stains, 

 is due to the existence in it of a proportionally large number of 

 non-stainable archoplasmic filaments. 



Having briefly sketched the general outline of the process by 

 which the characteristic shape of a caryokinetic figure originates, 

 it would be appropriate to devote a few words to the obscure 



