in the A irinial Kingdom. dll 



of the nucleus " a dlstiuct spindle, with delicate nuclear plate/' 

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

 " in c^eneral approaches the so-called indirect nuclear divi- 

 sion " *. Among the Ciliate Infusoria the micronuclei always 

 divide with mitosis "j". 



If we T)o\v wish to consider amitotic division in the Protozoa 

 we must first make a strict distinction between those 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 the former the amitotic division of the macro- 

 nucleus is an established fact, amoag the latter I know of no 

 case in whicli amitotic division was incontestably and indu- 

 bitably proved. 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 |, no 

 weight can be attached to any statement of earlier date, t 

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

 observation of Brandt [he. cif.), that direct nuclear division 

 occurs in the formation of swarm -spores of Sphserozoids, 

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

 matin elements and the outline of the spindle are difficult to 

 see, and that in consequence of the smallest imperfections in 

 preparation tlie former may 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 find that between the macronucleus 

 of the Protozoa and the meganucleus of the Metazoa {cf. 

 p. 366, note) manifold analogies § exist. The macronucleus 



* Eronn's ' Klassen iind (_)rdmiiijjen. — I. Biitschli, Protozoa ; II. Abt. 

 Mastigopbora,' p. 742. 



t lu Opalina ranarum, iu which, so far as we at present know, only a 

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

 been distinctly described by Pfitzner {" Zur Keruteikuig bei deu Proto- 

 zoen," Morphol. Jahrbuch, Bd. xi.). 



As the contour of the nucleus iu this instance is always distinct durino' 

 the mitosis, and consequ'i'ntly by the application of a faulty method of 

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

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

 severe criticism. 



X The development of the methods of preserving Protozoa and staining 

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

 Acad. Sc. Paris, t. Ixxxviii., 1879), E. Korsc-helt (Zonl. Anzeiger, no. 109, 

 1882), Landsberg (Zool. Anzeiger, no. 114, 1882), and A. (-iruber{Zeitschr. 

 f. wiss. Zoo!oo-ie, Bd. .38, 1882). 



§ The macro- and megmucleus have arisen iu two independent ways. 



