Herrick, Physiological Corollaries of Equilibfium Theory. 25 



tral nervous system. There is a form of vital equilibrium so 

 resident in the general system as to give rise to much the same 

 phenomena of nervous unity as in the case of higher animals. 

 It is not at all necessary to suppose that the cells of the body 

 of higher animals have lost this power during the differentia- 

 tion of the central system ; it would be more probable that the 

 central system should be superadded. 



There are a number of classes of cells which seem to be, 

 in the nature of the case, freed from all direct nervous control. 

 The chromatophores of the Amphibia, to which the writer has 

 devoted some study, seem in some cases not to be in a direct 

 way associated with a definite nervous supply.^ They are, in- 

 deed, literary migratory, though the scope and range of move- 

 ment remains to be worked out. Two things may be quite 

 positively stated ; first, that these cells are to some extent inde- 

 pendent of fixed nervous influence, and, second, that they are 

 very really under indirect nervous control. Experiments tried 

 in my laboratory many years ago showed that, in young cat 

 fish, section of a branch of one of the cranial nerves destroyed 

 the very marked adaptive power for the injured side. A fish, 

 originally black, when placed in an aquarium with yellow bot- 

 tom invariably changed to the color of the environment unless 

 the mutilation described prevented it. 



The observations of G. H. Parker on photometric changes 

 in retinal pigment cells of Palcsmonetes are interesting in this 

 connection in showing that exposure to light causes actual 

 changes in form and a segregation of the pigment of these cells. 

 He finds that section of the nerve or severing the eye stalk from 

 the body does not wholly prevent the reaction. This is an illus- 

 tration of a reaction exceedingly resembling a true nervous 

 response. 



The embryonic tissues of all animals possess this coordi- 

 nating sensitiveness and trophic interaction to a high degree. 

 In the extreme case afforded by the blood corpuscles and lymph- 

 ocytes it seems perfectly plain that there can be no direct 



1 Methylene blue seems to show connections in some instances. 



