No. 3.] STUDIES ON- CEPHALOPODS. 273 



plasmic fibrils, and that is the duplex activity of the archo- 



plasmic threads at two different periods of caryokinesis. In 



the first half of the process, the fibrils are distensible, stretching 



away from the archoplasmic centres, and in the latter half, the 



activity becomes just reversed and then become contractile, 



travelling towards the respective centres from which they arise. 



'strasb'lirger has always held that the archoplasmic spindle 



threads have a cytoplasmic origin, the threads penetrating the 



nucleus from two poles, through the porous nuclear membrane. 



In his more recent studies on Spirogyra} he conclusively supports 



his former conclusion. 



As to the origin and significance of the interzonal fibrils, 



Strasburger says : — ^ 



'' Augenscheinlich sammelt sich zwischen den beiden Kern- 

 plattenhalften ein osmotisch wirksamer Stoff an, der Zellsaft aus 

 der Umo-ebung an sich zieht und der die angrenzende Plasma- 

 hiille na'ch aussen treibt. Es lasst sich annehmen, das dieser 

 Stoff zuvor zwischen den Spindelfasern angesammelt war; ja ich 

 mochte noch welter gehen und die Vermuthung aussprechen, das 

 derselbe dem ursprunglichen Kernsaft entstammt." Through- 

 out the process of nuclear division the nucleus is enclosed by a 

 cytoplasmic mantle. As the two daughter nuclei separate 

 wider and wider, the equatorial achromatic space lying between 

 them assumes the swollen barrel shape, which is enveloped by 

 an extremely thin cytoplasmic bag. This interzonal structure is 

 designated as the Verbindungsschlauch, in which the equatorial 

 susp'^ensory threads appear prominent as pronounced ribs. This 

 - Verbindungsschlauch " constantly increases in length and 

 breadth by osmotic absorption of fluid through its walls. Stras- 

 burger offers the following suggestion in regard to the signifi- 

 cance of this structure: "Es unterleigt kaum emem Zweifel, 

 das wir in dem Verbindungsschlauche eine Einrichtung vor 

 uns haben, die mit Zuhulfenahme osmotischer Druckkrafte bei 

 Spirogyra dazu dient, die Zellkerne auseinander zu treiben, 

 sie in bestimmter gegenseitiger Lage zu erhalten, endlich den 

 Anschluss der gesammten Theilungssfigur an die vordringende 

 Scheidewande herzustellen " (pp. 21, 22). 



Strasburger, as has been seen, regards the interzonal filaments 



1 Ueber Kern- und Zelltheilung in Pflanzenreiche, etc. 18S8. 

 "^ loc. cit. p. 17. 



