DERIVED ORGANIZATION 89 



its different elements. These may be more or less independent in 

 their division, or they may be united in various simple or complex 

 combinations during the division processes. Or the nuclear ele- 

 ments may be combined with extranuclear cytoplasmic elements to 

 form a characteristic division figure representing a most highly 

 perfected mechanism for the equal distribution of the more impor- 

 tant cell elements which are thus perpetuated from generation to 

 generation by equal division. Such a perfected mechanism, termed 

 a karyokinetic or mitotic figure, is characteristic of nuclear division 

 in cells of the Metazoa and of higher plants, the combination of 

 processes whereby the constituent parts are equally distributed to 

 daughter cells being known as indirect division, karyokinesis, or 

 mitosis. In Metazoa such processes involve division of centrioles 

 and centrosomes, formation of a fibrillar spindle figure, dissolution 

 of the nuclear membrane, aggregation of chromomeres into compact 

 chromosomes which are identical in size, shape and number in cor- 

 responding cells of all individuals of the same species, and the 

 longitudinal division of each chromosome in all somatic cells, sepa- 

 ration of the daughter chromosomes and reconstruction of the 

 daughter nuclei. In all Metazoa the processes of mitosis differ 

 only in minor details and mitosis is the characteristic type of nuclear 

 division, although direct division, whereby the nucleus divides 

 without the formality of centrosomes and spindle or chromosome 

 formation is known in a few cases. 



In Protozoa, on the other hand, there is no one type of nuclear 

 diyision common to all forms. Here we find gradation, in the asso- 

 ciation of constituent nuclear and cytoplasmic kinetic elements 

 during division resulting in an enormous variety of division types. 

 These vary in complexity from a simple dividing granule to mitotic 

 figures as elaborate as in the tissue cells of higher animals and plants. 

 Some observers see in these diverse types a possible evolution of 

 the mitotic figure of Metazoa and use them as one would use the 

 separate pieces of a picture puzzle to reconstruct its past history 

 in development. Terms like "promitosis" (Naegler), "mesomito- 

 sis" (Chatton) and " metamitosis " (Chatton) may serve a useful 

 purpose to indicate general types of the association of nuclear and 

 cytoplasmic elements during division, but when an effort is made to 

 give a specific name to each step in an increasingly complex series 

 the result is a confusion of terms which defeats the useful purpose 

 intended. Thus Alexeieff proposes a large number of specific names, 

 not all his own, it is true, for protozoon division types which he 

 regards as sufficiently definite to permit of recognition. 1 



Because of the multitude of diverse types of division figures in the 



1 These terms include Promitosis, Proteromitosis, Haplomitosis, Cryptohaplomi- 

 tosis, Eurypanmitosis, Cyclomitosis or Polymitosis, Polyrheomitosis, Metamitosis, 

 etc. 



