ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 565 



generalization " omnis nucleus e nucleo " does not hold, for the nucleus 

 may arise de novo from extra-nuclear (chromidial) chromatin. In the 

 Protist cells a distinct nuclear membrane may be entirely absent ; the 

 chromatin is not necessarily confined to the nucleus ; the linin (alveolar) 

 framework of the nucleus is but little in evidence, if present at all ; the 

 chromatin may lie simply in a vacuole of nuclear sap ; if a true nucleus 

 is present it seldom shows a true (plastin) nucleolus, but usually a 

 karyosome or chromatin nucleolus ; or it may be granular, consisting of 

 a clump of small grains of chromatin. Many observations have shown 

 that the nucleus during life is undergoing continual internal move- 

 ments and rearrangements of its parts, and is by no means at rest. 



The simplest body that can be recognized as a nucleus, distinct from 

 chromidia scattered in the cytoplasm, is a mass of chromatin or a clump 

 of chromatin-grains supported on a framework and lodged in a special 

 vacuole in the cytoplasm. From this type the complicated forms may 

 be derived. But it must be noted that the nucleus is not a mass of 

 chromatin, but a cell-organ, of greater or less structural complexity, and 

 of unique function. 



Too much emphasis has been laid on the staining-reactions of 

 chromatin, but these are an " accident," though it may be an " in- 

 separable accident," not a " difference," which can be used to frame a 

 logical definition. Chromatin is rich in phosphorus-compounds, and 

 resistent to digestion, but the only criterion is its behaviour, its rela- 

 tions to the activity and development of the organism. In some simple 

 Protists, however, without definite compact nuclei, the identification of 

 chromatin may be very difficult. To a large extent we are thrown back 

 on staining reactions, and on the behaviour of the grains in question 

 during the process of fission. 



The cell is an organism, and often very complex in structure and 

 function. " The vital processes exhibited by the cell indicate a com- 

 plexity of organization and a minuteness in the details of its mechanism 

 which transcend our comprehension and baffle the human imagination, 

 to the same extent as do the immensities of the stellar universe." Thus 

 the phenomena of karyokinesis and maturation " give us, as it were, a 

 glimpse into the workshop of life and teach us that the subtlety and 

 intricacy of the cell-microcosm can scarcely be exaggerated." 



Without losing sight of the fact that the various parts of the cell are 

 indispensable for the maintenance of life, we may ask which are the 

 phylogenetically older. The cytoplasmic and chromatinic constituents 

 may have arisen as differentiations of some primitive substance, which 

 was neither the one or the other ; or one of the two constituents may 

 have been evolved from the other. No concrete foundation can be 

 found for the view that cytoplasm and chromatin have a common origin 

 in " plasson." Haeckel's Monera, as defined by him, are fictitious. All 

 those that have been recognized have been found to have nuclei or 

 nuclear substance. 



Boveri has suggested that chromosomes were primitively independent 

 elementary organisms which now live symbiotically with protoplasm, 

 and that the cell arose from a symbiosis between two kinds of simple 

 organisms. Mereschkowsky has assumed a double origin for organisms, 

 mycoplasm combining with amceboplasm. Biococci, minute ultra- 



