1 82 MARINE BIOLOGICAL LABORATORY. 



Boveri meets this difficulty by denying the filament- 

 ous nature of the interzonal substance, holding that 

 what appears as filamentous is the optical expression of 

 the longitudinal folds produced by the contraction of the 

 two antagonistic groups of archoplasmic fibrils, whose 

 distal extremities are fastened to the chromosomes. 

 Strasburger ascribes to the substance the function of 

 a wedge which grows in size by the absorption of the 

 cytoplasmic fluid, and pushes apart the parallel "plates" 

 of chromosomes. Platner explains the filamentous ap- 

 pearance of the interzonal substance as the optical ex- 

 pression of a protoplasmic stream. The existence of 

 such a stream in a living dividing cell has, however, 

 been denied by Strasburger. 



As to the filamentous nature of the interzonal sub- 

 stance, there can be no question, as several observers 

 have abundantly shown. My own studies on Cephalo- 

 pods and Echinoderms have convinced me of the 

 truth of this conclusion. Further, no optical difference 

 could be observed between the archoplasmic fibrils at 

 the poles of the spindle and the filamentous bodies in 

 the intermediate zone, which fact has already been 

 pointed out by several investigators. 



Observing, then, that the interzonal portion of the 

 caryokinetic figure consists of the bundle of filamentous 

 substance, that this filamentous substance is essentially 

 the same as the archoplasmic filaments of the spindle, 

 that the length of these filaments is exa'ctly the same 

 as the space between the parallel bands of chromosomes 

 in all stages, that the archoplasmic filaments have been 

 growing in length from the poles toward the equator of 

 the nucleus, and, further, that the interzonal filaments 



