METABOLIC GRADIENTS 6l 



in a relation to one or more of these gradients which is 

 definite and characteristic for each kind of organism. 

 The relation of the central nervous system to these 

 gradients is highly significant. The apical portion of 

 the central nervous system, the cephalic ganglion or 

 brain, always arises in the region of highest metabolic 

 rate in the whole body, the apical region of the major 

 axis, and such portions of the central nervous system 

 as appear in other parts of the body, e.g., the longitudinal 

 ganglionic nerve cords of various invertebrates and 

 the spinal cord of vertebrates, always arise in the regions 

 of highest rate in the minor axial gradients. In the 

 bilateral invertebrates this is the median ventral, in 

 the vertebrates the median dorsal, region. In short, 

 it may be said that where a central nervous system is 

 present it is the organ characteristic of the apical, i.e., 

 the dominant, region in each of the chief axial metabohc 

 gradients. The functional dominance of the central 

 nervous system in the later life of the animal is then 

 simply a more highly specialized expression of the 

 primary relation of dominance and subordination 

 existing at the beginning of individuation between 

 regions of high and those of lower metabohc rate. 



As regards plants, I have as yet examined only some 

 fifteen species of marine algae, but in all of these the 

 apical region of each axis shows the highest suscepti- 

 bility to the higher concentrations of cyanides and the 

 susceptibility decreases very markedly in the basal direc- 

 tion. In these plants there is no such disintegration at 

 death as in the lower animals, although in the more 

 transparent forms the breaking up and coagulation of 

 the protoplasm can be observed inside the cell. By first 



