REGULATORY PROCESSES IN ORGANISMS 181 
of these correlative factors show a high degree of specificity. 
Moreover, the chemical factors are by no means the only factors 
in correlation: mechanical and other physical factors also play a 
part. And finally, the experimental investigations themselves 
have demonstrated the importance of physiological correlation 
in morphogenesis. 
In short, there is at present every reason to believe that the 
existence and continuity in time and space of organic individuality 
are essentially dependent upon physiological correlation, 7.e., upon 
processes and conditions which are accessible to scientific seat: 
gation and analysis. 
3. The basis and nature of physiological correlation 
That physiological correlation is in general dependent upon the 
physical and chemical processes and conditions in the various 
parts which make up the individual cannot be doubted. These in 
‘turn are dependent upon the constitution of the parts, which itself 
depends in part upon preéxisting correlation and to a greater or 
less extent upon conditions and processes in the extra-individual 
environment. At every step in our consideration we recognize 
the mutual interdependence of constitution and correlation. 
But if we consider the organic individual only as it exists at 
the preseat time, then we may say that the existing physiological 
correlation between parts is dependent upon the conditions and 
processes in the parts, however these may have been brought 
about. 
In general we can recognize at present three main groups of 
correlative factors: first, mechanical or mass correlation (Roux, 
95, IL, p. 240), which results merely from the existence of mass 
without respect to constitution; second, substantial or material 
correlation, which consists in the actual transference or transpor- 
tation of substance possessing a certain physical or chemical con- 
stitution, e. g., chemical correlation; and third, dynamic correla- 
tion, of which the essential feature is the transmission of energy 
rather than the actual transportation of material over any appre- 
ciable distance. None of these forms of correlation can be sharply 
