No. 3.] STUDIES ON CEPHALOPODS. 269 



towards the equator" of the nucleus. In the first stage, the 

 nucleus retains the elliptical outline, with a complete nuclear 

 membrane, and two archoplasmic asters at the two antipodal 

 ends of the nucleus. In the second stage, the retraction of the 

 nuclear filaments towards the equator has commenced, and with 

 it, the rudiment of the archoplasmic spindle appears inside of 

 the nuclear membrane, presenting very much the same appear- 

 ance as in Fig. VII, p. 267, previously described. This retrac- 

 tion towards the equator goes still further in the third stage, 

 and with it the shape of the spindle becomes more perfect. In 

 the fourth stage, the nuclear filaments are reduced into a plate- 

 like structure, and the original cavity of the nucleus, still sharply 

 bounded by the nuclear membrane, contains the complete spin- 

 dle ; and in the succeeding figure (/) the metakinesis in its 

 advanced stage is represented. The resemblance of this series 

 of figures to the series I have already given is perfect. 



These observations, according to Carnoy, show two important 

 facts : — 



(i) The persistence of the nuclear membrane through the 

 stages of caryokinesis. 



(2) The developmental history of the spindle. After all this, 

 Carnoy,^ however, concludes, " lis prouvent d'abord que le 

 fuseau peut deriver exclusivement du noyau." 



It appears to me to say that the spindle is formed inside of 

 the nuclear membrane is one thing, but it is quite another to 

 infer from it that the spindle is derived from the nucleus. Why 

 may it not be formed by the invasion of the archoplasmic fila- 

 ments from the outside of the nucleus, through the porous 

 nuclear membrane, as was pointed out by Strasburger and 

 Guignard .'' 



I am strongly inclined to believe that the interesting series 

 of stages in the formation of the spindle and of the chromatic 

 equatorial "plate,'' given by Carnoy in the place above referred 

 to, belongs to the same order of facts presented in the previous 

 pages in connection with the origin of the spindle in the Cephalo- 

 pod blastoderm. May not the beautiful series of figures given 

 by RabP and Schewiakoff,^ showing the gradual formation of 



1 loc. cit. p. 317. 2 Rabl: Ueber Zelltheihmg. Morph. Jahrbuch., Bd. X. 



3 Schewiakoff : Ueber die Karyokineiische Kerntheilimg der Euglypha alveolata. 

 Ibid., Bd. XIII. 



