378 Dr. H. E. Ziej^-ler on Aniilotic Xucltir Dicision 



of the Protozoa is of the greatest importance for nourishment 

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

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

 ribbon or wreatli of roses. With regard to tlie distribution of 

 chromatin it exhibits a certain similarity to the meganuclei 

 of the Metazoa. The 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 possil)le divisions is not unlimitel, and that, as stated by 

 IJiitschli and ^laupas {Inc. cit. p. 400), on the basis of breeding- 

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

 the existing niacronucleus nndcrgoes 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 .Metazoa amitotic division indicates the near 



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

 Acinetaria luu.-t be regarded as terminal branches of tbe Pi-olozoon stem, 

 which grow no liigher ; tlie root ot" the Metazoa does not proceed from 

 tbese branches of the Protozna, and to bring the meganuclei of the Meta- 

 zoa and the macrouuclei of the Protozoa into dire-t phylogenetic relation- 

 ship Avith one anotlier is entirely inadmissible. 



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

 frequently been distinguished as tlie sexual nucleus, and the inacronucleus 

 as the metabdli^m-nucleus [cidi' liiitsclili, 'Protozoa, III. Abt. Infusoria,' 

 p. 1043). Compare also the statements of II. Ilertwig, •• L'eber die 

 Koniugati(m der Inhisorien," Abhandl. d. k. Akademie, Miiuchen, II. KJ. 

 17 lid., 18S9, p. :.nt) et seqq. 



t Maupas ("he rajeimissement caryogamique chez les cili^s," Archives 

 de Zoologie, exp. et gen. 2 set. t. vii., I8t^5r». x. p. 444) writes: — "An 

 extremely imiiurtant cnurequeuce results from the growth of the uew 

 macronuclei. 'I'lie>e nuclei in j^oiut of tact lose th'- faculty of dividing bv 

 karvoniitosis, and heucet.u-ward only multiply by simple con.-tiicliou. 

 At the same time tiieir function, having beeome ])urely vegetative, will 

 be contined to the control of nutrition, growth, and agamic multiplica- 

 tion. They have entirely lost the faculty vf rejuveuating earvogamv." 



X Mau])as (At. cit. ]>. 44ti), writes : — "• The mode of eliminating the 

 old nucleus differs slightly according to the species. In Votjmlium .... 

 the wlmle becomes disorganized at once, and -rradually iliss ilves by a slow 

 absorpti-'U, resi'mbliug actuil digestion. In the • txyiricliida', L.txoplivi- 

 lidie, Kuplotid;e, and \'ortiivllid;e this al)sor]ition is preceded by a frair- 

 nienlatiou ; lastly, in the two lar^'e I'lirainccin pr.paration is made for 

 the fraiiineutation itself by a preliminary unroUiuvr of the nuclear nutss, 

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

 the dissolution of the macrouudeus will be found in lUitsclili, lor. cit. 

 p. PU3. 



