ill the Aiiliiinl KiHijiiiin. ^11 



of tlic nucleus " a distinct s))in(lle, with delicate nuclear ])late," 

 and he is of the opinion that nuclear division in the Flagellata 

 ** in £:eneral approaches the so-called indirect nuclear divi- 

 sion " *. Anionic; the Ciliate Infusoria the micronuclei always 

 divide with mitosis \. 



If we now wisli to consiiler amitotic division in the Protozoa 

 we must first make a strict distinction between tliose Protozoa 

 which at the same time contain both a macro- and a micro- 

 nucleus and those in which only a single kind of nucleus is 

 ]»resent. In th(; t'oriner the amitotic division of the macro- 

 nucleus is an establish.3 1 fact, among the latter I know of no 

 case in whicli amitotic division was incontestably and indu- 

 bitably j)rov^;d. As it is only since the commencement of 

 the eighties that Protozoa have been treated by such methods 

 of conservation and staining, that the disposition of the chro- 

 matin in the division of the nucleus can be made out J, no 

 weight can be attached to any statement of earlier date. E 

 am also unable to attach any great weight to the more recent 

 ol)servation of Brandt {loc. cit.), that direct nuclear division 

 occurs in the formation of swarm -spores of Sphterozoids, 

 having regard to the fact that in such small nuclei the chro- 

 matin elements and the outline of the spindle are difficult to 

 see, and tliat in consequence of the smallest imperfections in 

 preparation tlie former niay become clotted together. 



If we now turn to the Ciliate Infusoria and the Acine- 

 taria, in which a micronucleus (small or secondary nucleus 

 [" Kleinkern, Nebenkern "]) and a macronucleus (large or 

 primary nucleus [" Grosskern, Hauptkern "]) exist, and 

 consider the morphological properties and the function of the 

 macronucleus, we shall Hnd tliat between the macronucleus 

 of the Pr;)tozoa and the meganucleus of the Metazoa (c/! 

 p. o'oQj noie) manifold analogies § exist. The macronucleus 



* Bronn's ' Klasseti uud (_)nlimii;ren. — I. Biitschli, Protozoa : II. Abt. 

 Mastiprophora,' p. 742. 



t In Opalina rtaiarum, in which, so far as we at present know, onlv a 

 single form of nuclei, and not both kinds, occurs, mitotic division has 

 been distinctly described bv Pfitzner (" Zur Kernteiluug bei den Proto- 

 zoeu,"' Morphol. .lahrbnch, Rd. xi.). 



As the contour of the nucdeus in this instance is always distinct durin"' 

 the mitosis, and consequMitly by the application of a faulty method of 

 staining the division would appear to be direct, we have the greater rieht 

 to submit the statements as to direct nuclear division in Protozoa to a 

 severe criticism. 



X The development of the methods of preseiwing Protozoa and stainin(y 

 their nuclei is marked by -the publications of A. Certes (Couipt. Rend. 

 Acad. Sc. Paris, t. Ixxxviii., 1-^79), E. Korsehelt (Zonl. Anzeiger, no. 10.9, 

 1882), Laud.*berg (Zool. Anzeiirer, no. 114, 1882). and A. Graber(Zeit,schr. 

 f. wiss. Zoo'f.gi-, Rd. .3-^, 1882). 



§ The macro- and me^;- muoleus have arisen in two independent wavs. 



