158 RALPH S. LILLIE. 



this action on the basis of transport of actual materials through 

 the flow of sap, blood, or other circulating medium are in many 

 cases patently inadequate. Consider to take an extreme in- 

 stance the transmission of chemical influence from the brain 

 to a secreting gland-cell; here obviously the problem of the 

 nature of physiological conduction enters; and it is more espe- 

 cially this problem the nature of transmission of physiological 

 influence where no direct transmission of material is possible 

 upon which experiments of the above kind appear to throw light. 

 The problem is plainly a most fundamental one, since physio- 

 logical coordinations of the most varied nature depend upon the 

 rapid conduction of chemical influence between different parts 

 of the organism. The integration of the whole complex system 

 of structures and chemical reactions into a unified and regularly 

 acting living organism probably depends more essentially 

 upon transmission of this type than upon any other single 

 process. 



The transmission of formative influences, sometimes of a 

 growth-inhibiting, sometimes of a growth-promoting kind, from 

 one region of the organism to another is a well-known phe- 

 nomenon in both animals and plants. Usually it has been 

 explained either as due to the production and transport of 

 special materials (organ-forming substances, hormones, etc.), 

 or as due to changes in the distribution of materials already 

 present (changes in the flow of water in plants, increased avail- 

 ability of nutritive substances to one organ when another organ 

 is removed, etc.). In animals a special role has at times been 

 assigned to nervous influences; the nervous system 1 or sense- 

 organs 2 have been shown in some cases to influence the rate of 

 regeneration, i. e., a transmissive instead of a transportative 

 means of control 3 has been recognized; but in plants explana- 

 tions based upon the assumed existence of form-determining 



1 This influence is seen (e. g.) in Herbst's experiments in which the regeneration 

 of the eye in Crustacea was found to depend on the presence of the optic ganglion; 

 also in planarians and other forms. 



2 The presence of the marginal sense organs in regenerating pieces of the medusa 

 Cassiopea favors regeneration, according to the recent observations of Gary, 

 Journ. Exper. Zool., 1916, Vol. 21, p. i. 



3 For a discussion of the general nature of this influence see Child's "Individu- 

 ality in Organisms," especially Chapter 6. 



