378 Dr. H. E. Ziegler on Auiilotic Nucle.ir Dioisioa 



of the Protozoa is of the greatest importance for nourishment 

 and growth *. It is distingnished by its remarkable size t, 

 and in hirge Protozoa assumes a branched shape or that of a 

 ribbon or wreath of roses. With regard to the distribution of 

 chromatin it exhibits a certain simihirity to the meganuclei 

 of the Metazoa. Tlie process of division may be simply 

 described as direct, or, with reference to the longitudinal 

 streaking and finely fibrillar structure which appears in the 

 dividing nucleus, as an intermediate stage between mitotic 

 and amitotic division. It is very probable that the number 

 of possible divisions is not unlimited, and that, as stated by 

 Blitschli and Maupas [loc. cit. )>. 400), on the basis of breeding- 

 experiments, conjugation must set in from time to time, when 

 the existing macronucleus undergoes dissolution \ and is 

 replaced by one newly formed. As in the Metazoa, so there- 

 fore in the Protozoa also, amitotic division appears only in the 

 case of those nuclei which perish after a certain time ; it is 

 true that a large number, even several hundreds, of divisions 

 may ensue before regeneration becomes necessary, while 

 among the JMet;tzoa amitotic division indicates the near 



We may not speak of an homology, because the Ciliate Infusoria and the 

 Acinetaria mii>t be re<>^arded as terminal branches of the Pvotozoon stem, 

 which grow no higher ; tlie root of the Metazoa does not proceed from 

 these branches of the Protozoa, and to bring the meganuclei of the Meta- 

 zoa and the macronuclei of the Protozoa into direct phylogenetic relation- 

 ship with one another is entirely inadmissible. 



* Latterly, following the example of Blitschli, the micronucleus has 

 frequently been distinguished as the sexual nucleus, and the macronucleus 

 as the metabolism-nucleus [vide. JJiitschli, ' Protozoa, III. Abt. Infusoria,' 



J). Iti43). Com])are also the statements of R. Hertwig, " Ueber die 

 vonjugation der lufusorien,'' Abhandl. d. k. Akademie, Miinchen, II. Ivl. 

 17 lid.; 1889, p. -im et .'^eqq. 



t Maupas (" Le rajeunissement caryogamique chez les cilies," Archives 

 de Zoologie, exp. et gen. 2 ser. t. vii., 1889, x. p. 444) writes: — "An 

 extremely important CdU.-equence results from the growth of the new 

 macronuclei. These nuclei in joint of fact lose the faculty of dividing by 

 karyomitosis, and hencefiu-ward only multiply by simple constiiction. 

 At the same time their function, having become purely vegetative, will 

 be confined to the control of nutrition, growtli, and agamic multiplica- 

 tion. They have entirely lost the faculty of rejuvenating caryogauiy." 



X Maupas {Inc. cit. p. 440), writes: — "The mode of eliminating the 

 old nucleus diifers slightly according to the species. In Coljndium .... 

 the whole becomes disorganized at once, and gradually dissolves by a slow 

 absorption, resembling actu il digestion. In the Uxylrichidie, Loxophvl- 

 lidfe, Euplotid*, and Vorticellidie this absorption is preceded by a frag- 

 mentation ; lastly, in the two large Paramecia preparation is made for 

 the fragmentation itself by a preliminary unroUino- of the nuclear mass, 

 which becomes drawn out into long ribbons." A detailed description of 

 the dissolution of the macronucleus will be found in lUitschli, loc. cif. 

 p. 1G13. 



