1 84 MARINE BIOLOGICAL LABORATORY. 



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 opposing systems of the archoplasmic fila- 

 ments behaving in a similar way, and lengthening in a 

 contrary direction, would reduce the spherical nucleus 

 first to a bi-concave disc, then to a Hat ** plate," and 

 finally, into two parallel ''plates," each ''plate" travel- 

 ling in an opposite direction. The interzonal filaments, 

 then, according to this view, are the actual continuations 

 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. Intei'zonal 

 filmnents are, therefore, the prolongations of the iiit^-a- 

 miclear 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 caryo- 

 kinetic figure originates, it would be appropriate to 

 devote a few words to the obscure point as to the origin 

 and movement of the archoplasm itself. But as a matter 

 of fact, we know as yet very little in regard to the origin 

 of the archoplasm, sometimes wdth a definite body in 

 its centre — the cciitrosome. A great authority like van 

 Beneden looks upon it as a permanent organ of the cell, 

 equal in value to the nucleus itself ; but the whole ques- 

 tion of its origin and its apparent homologues, which 

 pass by different names in different cells, is too compli- 

 cated and obscure to be discussed in this place.. 



