ZOOLOGY SINCE DARWIN. 483 



structure and should not, without further evidence, be compared to an 

 albuminoid mixture. 



By this time the enthusiasm which hailed bathybius as the represent- 

 ative of Oken's "primitive slime," an undifferentiated protoplasmic 

 mass covering' the bottom of the ocean, has considerably cooled. 1 The 

 alleged nonnucleated primitive beings disappear more and more since 

 we have had the means of demonstrating the cell nucleus where it had 

 escaped observation when treated by the technical methods formerly 

 used, and the hypothesis of "free cell formation' 7 in organic fluids has 

 given place to the maxim "omnis cellula e cellula." 



There will, then, on the day when we learn that the last of the inoners 

 possesses a nucleus like other cells, be seen a much greater gap between 

 the simplest known living being and the inorganic individual — the 

 crystal — than is realized to-day. 



Zoology has obtained more satisfactory results from the numerous 

 researches, which, either with or without the knowledge of their con- 

 ductors, contributed to bring nearer to a solution the problems of 

 heredity and variation. 



Darwin considered heredity as a fact of experience demonstrated by 

 the specific similarity of child and adult, without attempting to seek 

 for its material vehicle. 2 Since, however, all living beings are made up 

 of cells, and even the most complicated organism has at the beginning 

 of its development the morphological value of a single cell, such a 

 vehicle can be only a part of a cell. To find it we must have a deeper 

 insight into the structure of the cell and into the significance of its 

 various parts. 



For example, as soon as the structure of the cell substance and that 

 of the nucleus which it contains were investigated by the new methods, 

 the surprising discovery was made that movement and irritability, as 

 well as respiration, are functions that the cell substance exercises inde- 

 pendently from the nucleus; that, on the contrary, assimilation and 

 secretion take place only under the influence of the latter and that the 

 nucleus is the only organizing morphogenic factor of the cell. Further 

 investigations showed that the cell consists of two substances, chro- 

 matin and achromatin, distinguished by their behavior with staining 

 fluids, the first of which plays an important role in cell division, as its 

 distribution inaugurates the multiplicative process and leads through 

 a regular succession of metamorphoses (mitosis) first to the bipartition 

 of the nucleus, and then to that of the extranuclear cell substance. 



1 The bathybius, recently discovered by Bessels, appears to be nothing more than 

 a plasmodiuin-like organism having only a local distribution. (See Bronn's Classen 

 und Ordnungen des Thierreichs, Protozoa, recently reedited by O. Biitschli, pp. 

 179-181. Leipzig and Heidelberg, 1880. . 



'-The pangenesis hypothesis of Darwin, which supposed that the germ was 

 influenced by the form of the body which held it as well as by external conditions 

 of existence by means of small particles attracted to it from all parts of the body, 

 is without any evidential basis, and is, as Weismann (Germplasma, p. 7) has 

 remarked, more a statement than a solution of the question of heredity. 



