No. 3.] STL/DIES OAT CEPHALOPODS. 271 



" D'ou vient rimpulsion qui determine le d^doublement des 

 corpuscules centraux, la formation des cordons pelotonnes et la 

 division longitudinale des anses ? Reside-t-elle dans le noyau, 

 ou dans le corps cellulairc ? Aucune donnee positive ne permet 

 de resoudre cette question. Nous n'avons reussi a etablir que 

 deux choses : cest r existence dafis la celhde d'nn appareil ou 

 dim ni^caiiisme qui preside a la division cellnlaire, comme notre 

 systbne vinscjilairc a la locomotion, et le dMonblement de ce 

 m^canisme pr^alablement a la division nneUaire.'^ 



To this must be added his account of the origin of interzonal 

 fibrils. As van Beneden 1 observes, with the division of the 

 equatorial chromosomes and their respective migrations towards 

 opposite poles, there comes into existence, intercepted by two 

 daughter "plates," a lamina, which he calls the "lame interme- 

 diaire," and the substance which composes it, the " substance 

 intermediarc''' (p. 543). 



This substance is described as being " relativement sombre 

 et chromophile, mais se colorant de moins en moins au fur et a 

 mesure que I'ecartement [of daughter chromatic stars] progresse " 

 (p. 556). 



As the separation of the chromatic loops progresses, one can 

 positively ascertain the existence of achromatic fibrils in this 

 intermediary substance. To these achromatic fibrils van Bene- 

 den gave the name of the "filaments reimissants," to distinguish 

 them from the achromatic spindle fibrils directly arising from 

 the spJih'es attractives (pp. 557, 558). 



As to the origin of the entire achromatic spindle, van Beneden 

 considers it as highly probable that it is derived from two sources, 

 a part from the spheres attractives (cytoplasmic in their origin), 

 and a part from the achromatic part of the nucleus. 



The achromatic constituent of the nucleus contributes to the 

 formation of the substatice ijiterme'diare with its fibrils, while 

 the ends of the spindle are derived from a portion of the attrac- 

 tive spheres. The gradual lengthening of the achromatic fibrils 

 in the interzonal space is due to the antagonistic pulling forces 

 emanating from the attractive spheres which act through the 

 contractile fibrils whose distal ends are attached to separating 



1 E. van Beneden: Recherches sur la maturation de Vceiif et la fccondation. 

 Archives des Biologic, Tome IV, 1883. 



