152 NUCLEI OF ANIMAL AND VEGETABLE CELLS. 



gated parent-structure and become at length the daughter- 

 nuclei, increasing, as van Beneden asserts, at the expense of 

 the substance which has ah'eady collected about the tips of 

 the original nucleus. 



Although Hertwig in his hardened and stained specimens 

 does not certainly speak of the derivation of the young nuclei 

 from the first median thickened zones, there can hardly be a 

 doubt that the lateral thickened zone (which afterwards became 

 the nuclei) correspond entirely to the segments of the nuclear 

 disc described by Biitschli, Strasburger, and Beneden, and 

 resulted from division of the former zone. 



In a paper in which the names of so many histologists 

 have been mentioned as in this, it would be unfair to omit a 

 reference to the researches of two observers who were among 

 the first to note certain of the new phenomena. FoU and 

 Flemming^ have described the appearance of two stellate 

 figures, which the former calls ' centres of attraction,' in cells 

 which are about to divide. Between these for a time certain 

 structures, supposed by them to be the remnants of the old 

 nucleus, are demonstrable by means of reagents (Fol used 

 acetic acid, Flemming carmine). During and after division 

 of the whole cell the new nuclei develope either in the fusion 

 of several vacuoles in the centre of the star-like figures (Fol), 

 or as new carminizable structures which appear in the same 

 situation (Flemming). It is hard to resist the conclusion 

 that the intermediate structures seen by Fol and Flemming 

 were the same with those described by others as portions of 

 the dividing primary nucleus. 



The researches which have been considered represent an 

 important step in the progress of histological inquiry 

 — a step which now awaits the confirmation of a more 

 numerous series of observations. 



* Tol : " Die erste Entwicklung des Geryonideneies," * Jenaische Zeitsch. 

 f. Med. u. Naturwiss,' Bd. vii, 1873. 



"^ Flemming : " Ueber die ersten Entwicklungserscheinungen am Ei der 

 Teichmuschel," ' Archiv. f. Mikros. Anat.,' Bd. x. " Studien in der Ent- 

 wicklungsgesch. der Najaden," ' Sitzb, der K. Acad. d. Wissensch,' iii, 

 Abth., Jabrg, 1874, Bd. kxi. 



