20 • SEGMENTATION. 



quoted by Flemming*. Schultze saw the nucleus assume a 

 duinb-bell shape, divide, and the two halves collect themselves 

 : together. The whole process occupied a minute and a half and 

 was shortly followed by the division of the Amoeba, which occu- 

 pied eight minutes. Amongst vegetable cells the division of the 

 nucleus seems to be still rarer than with animal cells. Sachs' 

 admits the division of the nucleus in the case of the paren- 

 chyma cells of certain Dicotyledons (Sambucus, Helianthus, 

 Lysimachia, Polygonum, Silene) on the authority of Hanstein. 



The division of the nucleus during cell-division, though 

 seemingly not very common, must therefore be considered as 

 a thoroughly well authenticated occurrence. 



The frequent disappearance of the nucleus during cell- 

 division is now so thoroughly recognised, both for animal and 

 vegetable cells, as to require no further mention. 



In many cases the partial or complete disappearance of the 

 nucleus is accompanied by the formation of two peculiar star- 

 like figures. Appearances of the kind have been described by 

 Fol^ Flemming^ Auerbach^ and possibly also Oellacher^ as 

 well as other observers. 



These figures' are possibly due to the streaming out of 

 the protoplasm of the nucleus into that of the cell I The 



^ Entwicklungsgeschichte der Najaden, lxxi. Bd. der Sitz. der k. Akad. Wien, 

 1875. 



5 Text-Booh of Botany, English trans, p. 19. 



^ Entw. d. Geryonideneies. Jenaische Zeitschrift, Bd. vii. 



* Loc. cit. 



^ Organologisclie Studien, Zweites Heft. 



* Beitrcige z.Eiitxoicklungsgeschichte der Knochenfischen: Zeit. fi'iT Wiss. Zoo- 

 logie. Bd. xxii. 1872. 



y The meraohs of Anerbach and Strasbnrger (Zellbildung u. ZeUtheihing) 

 have unfortunately come into m}' hands too late for me to take advantage of 

 them. Especially in the magnificent monograph of Strasbm-ger I find drawings 

 precisely resembling those from my specimens already in the hands of the 

 engraver. Strasbnrger comes to the conclusion from his investigations that the 

 modified nucleus always divides and never vanishes as is usually stated. If his 

 views on this point are correct part of the hypothesis I have suggested above 

 is rendered unnecessary. The striae of the protoplasm, which in accordance 

 with Auerbach's view I have considered as being due to a strcammg out of the 

 matter of the nucleus, he regards as resulting from a polarity of the particles 

 in the cell and the attraction of the nucleus. My own investigations though, 

 as far as they go, quite in accordance with those of Strasbnrger, do not supply 

 any grounds for deciding on the meaning of these striae; and in some re- 

 spects they support Strasburger's views against those of other observers, since 

 they demonstrate that in Elasmobranchs the modified nucleus does actuaUy 

 divide. 



8 This is the view which has been taken by Anerbach {Orgaiwlogische 

 Studien). 



