NUCLEI OF ANIMAL AND VEGETABLE CELLS. 151 



the same objects hardened and carminized. Differences of 

 hypothesis could hardly be avoided. 



Although it required the perfection of modern instruments 

 and technical methods to furnish a complete history of cell- 

 division, yet certain stages of it had already been dimly or 

 partially seen by earlier observers. Thus Bagge,i Gabriel,^ 

 and Kolliker^ have figured appearances similar to those 

 X shown in Plate! (figs. 5 — 7), which were thought to be due 

 to the division of the central nucleus into two. Moreover, 

 the first-mentioned author describes an elongation of nucleus 

 which resulted in the formation of a finger-biscuit-shaped 

 mass, and ultimately in its division into two parts. Again, 

 the radiate arrangement of the granules in the protoplasmic 

 cell-mass has been from time to time noticed as accompany- 

 ing cleavage, viz. by Derbes"* in the case of Eohinoderms, and 

 by Krohn^, Kowalewsky,^ and Kupffer^ in Ascidians. 



Of the changes affecting the nucleus during its elongation 

 Auerbach saw nothing but the collection of a clear, stellate 

 mass at its tips, which he thought to be due to the expulsion 

 of its contents, and an appearance as of two movable vacuoles 

 in the intermediate band. Among the rest the chief point 

 of distinction is that Hertwig describes no structure equiva- 

 lent to the cell-plate of Strasburger and Van Beneden, which 

 assists in the partition of the whole cell. It is important to 

 add, however, that Balfour,® in the fusiform nuclear struc- 

 tures which he describes as taking part in cell-division 

 under certain circumstances, represents an equatorial double 

 row of granules, between which the line of division of the 

 cell undoubtedly passed. 



The difference of opinion as to the origin of the nuclei of 

 the new segments is very well marked. Auerbach, as we 

 have already seen, regards their origin as palingenetic : the 

 nuclear substance, dispersed for a time throughout the cell- 

 mass, is re-collected into the vacuoles, which will become the 

 young nuclei. Strasburger and van Beneden are equally 

 explicit. According to them, the two halves of the nuclear 

 disc or essence nucleaire move to the extremes of the elon- 



' Bagge, ' Diss, inaug. de Evolutione Strongyli, &c./ Erlangen, 1S41. 



^ Gabriel, ' De Cucullaui Elegantis Evolutioue,' Berolini, 1853. 



3 Koliiker, ' Miiller's Arciiiv,' 1843. 



■• Derbes, loc. cit. 



* Krohn, "Ueber die Entwick. der Ascidien," 'Archiv f. Anat. u . 

 Phys./ 1852. 



^ Kowalewsky, ' Mem. de I'Acad. imp. de St Petersburg,' tome x. 



'■ Kupffer, "Die Stammesverwaudtschaft zwiciiea Ascidien u. Wirbel- 

 thieien," ' Archiv f. Mikro. Aaat.,' Bd. vi. 



^ F. M. Balfour, loc. cit. Ta,.^ a^, ,4^41 :...--' i. 



