232 DEVELOPMENT OF ELASMOBRANCH FISHES. 



evidence is quite conclusive are not very numerous. Recently 

 F. E. Schultze 1 appears to have observed it in the case of an 

 Amoeba in an altogether satisfactory manner. The instance is 

 quoted by Flemming 2 . Schultze saw. the nucleus assume a 

 dumb-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 Amceba, which occu- 

 pied eight minutes. Amongst vegetable cells the division of the 

 nucleus seems to be still rarer than with animal cells. Sachs 3 

 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 4 , Flemming 5 , Auerbach 6 and possibly also Oellacher 7 as well 

 as other observers. 



These figures 8 are possibly due to the streaming out of the 



1 Archivf. Micr. Anat. xi. p. 592. 



2 "EntwicklungsgeschictederNajaden,"LXXl.Bd.der5zV2.^r.^<ra</. Wim, 1875. 



3 Text-Book of Botany, English trans, p. 19. 



4 "Entw. d. Geryonideneies." Jenaische Zcitschrift, Bd. VII. 

 6 Loc. cit. 



6 Organologische Studien, Zweites Heft. 



7 "Beitrage z. Entwicklungsgeschichte der Knochenfischen." Zeit. fiir Wiss. 

 Zoologie. Bd. xxn. 1872. 



8 The memoirs of Auerbach and Strasburger (Zellbildung a. Zelltheilung) have 

 unfortunately come into my hands too late for me to take advantage of them. Especi- 

 ally in the magnificent monograph of Strasburger I find drawings precisely resembling 

 those from my specimens already in the hands of the engraver. Strasburger 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 proto- 

 plasm, which in accordance with Auerbach's view I have considered as being due to a 

 streaming 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 



