180 Cc. M. CHILD 
introduction of the experimental method into zodlogy has already 
demonstrated the limited scope and value of pure morphology 
for the interpretation of life. In the organism as we find it, the 
two factors, constitution and correlation are mutually determining. 
We cannot alter the constitution without altering the correlation 
of parts, neither can we alter correlation without changing con- 
stitution to a greater or less extent. The cases of so-called self- 
differentiation constitute no real exception to this statement,' 
which has the value and significance of a law of nature. Morphol- 
ogy and physiology are inseparable except analytically and their 
artificial separation can lead only to the formulation of many 
pseudo-problems and to uncertain or false conclusions and hypo- 
theses. 
In so far as the organism is a physiological, 7. e., a physico- 
chemical individual or unity, in so far must physiological correla- 
tion exist between its parts in the form of actual physical and chem- 
ical processes, conditions and substances. Until it is proven by the 
profoundest investigation and the strictest analysis that physiolog- 
ical correlation does not suffice to account for the organic indi- 
vidual, there is no need of turning to the vitalistic hypotheses for 
an interpretation. 
Indeed our knowledge of physiological correlation is in its 
earliest stages. One need only refer to the work on the conduction 
of stimuli in plants and through protoplasm in general and to the 
investigations of recent years on the thyreoid, the adrenals, the 
reproductive organs, the pancreas, etc., as organs of chemical 
correlation and to the work on hormones, to become aware of the 
advances in knowledge along this line within the last few years. 
At present we are willing to believe, in fact we find it difficult 
not to believe, that every metabolically active organ in the body 
is an organ of chemical correlation. And we also know that many 
1 As Roux (’95, p. 822 etc.) has pointed out development depends primarily 
upon correlation and absolute self-differentiation cannot occur. In cases where 
’ parts differentiate in a relatively high degree of independence from each other, we 
must believe, and in some cases, e.g., the nemertean egg, we know that this condi- 
tion is preceded by, and is the result of an earlier condition in which the parts are 
in much closer correlation. 
