Form Regulation in Harenactts pies Oc! 
differences, i. e., the heteropolar phenomena and the quantitative 
axial or polar differences, i. e., the differences between the two ends 
of the piece in primary heteromorphosis are determined by the 
correlations existing between parts after isolation. Preéxisting 
constitution and present correlation are then the two factors or 
factor-complexes which determine the phenomena of physiological 
polarity as they exist in regulation. 
These two factors are in other words the morphological and 
physiological aspects of the problem of polarity. I believe that 
every problem of morphogenesis possesses these two aspects and 
that any attempt either at purely morphological or purely physio- 
logical interpretation must of necessity be incomplete. When we 
assume the structural basis as given we may say that all problems 
of morphogenesis are physiological or functional in character, as 
I have done in certain papers. When we assume the various 
processes as given morphogenesis becomes a morphological prob- 
lem. But strictly speaking living structure without function 
and function without structure are alike inconceivable: changes 
in structure must accompany changes in function and changes in 
structure cannot occur without producing changes in function. 
Recent criticisms of some of my work remind me that it is_per- 
haps necessary, to emphasize once more the fact that I am using 
the word function in its broadest sense as synonymous with process 
or activity. 
III SUMMARY 
1 In the csophageal region of Harenactis tentacles and disc 
are always formed at the aboral as well as the oral ends of pieces, 
provided the pieces live long enough and become sufhciently dis- 
tended. The aboral mouth in these cases is not a new formation 
but is the result of fusion of the cut end of the body-wall with the 
cut end of the cesophagus so that the latter remains open. 
2 Complete or partial aboral discs develop inthe cesophageal 
region according as the operation involves the whole cross-section 
of the body or only a part of it. 
3. The formation of aboral tentacles is less rapid than that of 
