in the ^Iniimd Kiiiyiloin . 87i) 



ji|i])roach ot the end of the clivif^ioiis ; nevertliele.ss it must at 

 flie same time be remarked tliat the amitotic division of the 

 niaeromudous runs a more reguhir course and stands much 

 nearer to mitotic division than the typical cases of amitotic 

 division which occur in the MctazDa. 



It wouhl not be quite correct simply to assert that in the 

 Pnitozoa direct nuclear (livisi(jii is followed by division of the 

 cell, because before a ciliated [nfusorian or an Acinetariari 

 divides a double nuclear division takes place — the direct 

 division of the maeronuelcus and the indirect of the micro- 

 nueleus *. 



It follows fiom what has been stated that also in Protozoa 

 amitotic division, in so far as we know it at present, is seen 

 not as the ))rimeval method, but as that which is of secondary 

 origin. We have therefore now no empirical ground for the 

 view that indirect nuclear division lias originated phylogene- 

 tically trom direct. The question as to the earliest origin of 

 mitosis leads to that of the earliest origin of the nucleus, and 

 is equally obscure. 



Freibiir^'- i. B., Zoulegical Iiistituto of the University, 

 April 1891. 



Pobtscviiit. 



A short time before I received the pi oof-sheets of this paper 

 there appeared M. Loewir's treatise on " Pegenerati(jn and 

 Constitution of the White Blood-corpuscles " (" Neubildung 

 und Beschalienheit der weissen Blulkorperchen," Ziegler's 

 Beitrage zur palhol. Anatomie und allg. Pathologic, 10 Bd., 

 1891, p. 210), in which it is stated that the cells which Hoat 

 in the blood of the crayfish alw ays exhibit amitotic nuclear 

 division ; this nuclear division is frequently followed by 

 division of the cell, but multinuclear cells also occur. It 

 appears to me that no objection can be derived from these 

 observations against the statements which I have made above: 

 for, in the first place, Loewit himself gives a detailed descrip- 

 tion of the secretory nature of the cells of thecraytish's blood ; 

 he mentions that " in the cell-body of numerous cells of the 

 craytish's blood in the fresh state glistening drop-like 

 structures of varying form and size, and resembling fat, are 



• Since in many Acinetaria, and especially in the swarm -spores of 

 Porlojjhri/a, niieromiclei have been shown to exist (cide Biit>chli. loc. cit. 

 p. 187;J ; Maupas, /•■(■. cit. p. 3So), the well-known constricting-ott' oi the 

 nucleus in tlie foiniation of the swarm-spores oi Podojyhrya simply repre- 

 sents the division of the macrouucleu?. 



