690 JULIAN 8. HUXLEY 
follows: the Echinus rudiment at the start grows concomi- 
tantly with the Pluteus. After a certain time, however, it 
becomes so large that its weight drags the larva to the bottom. 
Here the conditions, as regards both food and general environ- 
ment, are unfavourable to the pluteus tissues; these begin 
to dedifferentiate, and as soon as they have passed a certain 
critical stage in the process the Echinus tissues become dominant 
and are able to develop further at the expense of the larval 
organization. In the broadest terms the balance im Amphibia 
is regulated mainly from within, in Echinoids mainly from 
without ; but in both cases the possibility of the sudden 
change which we call metamorphosis depends on the co-existence 
of two systems in the same organism which are very closely 
balanced as regards physiological dominance. 
To sum up, we may say that the facts of physiological 
dominance of inhibition of growth, of resorption, and of the 
state of balance which exists among the parts of any organism 
and is the dynamic expression of Roux’s ‘ Kampf der Teile’, 
are all intimately connected. As a matter of fact physiological 
dominance is rendered most obvious when it can be reversed, 
as in Perophora or in metamorphosis—and that is when the 
balance between sub-systems is very close. 
The various examples discussed may perhaps be made 
clearer by the use of symbols. In every case let A =a dominant 
system; B a system normally subordinate to A; C one 
normally subordinate to B and also to A. An arrow | indicates 
dominance, pointing towards the subordinate system. Brackets 
( ) indicate subordinate condition. Dashes (A’, B’, &c.) 
indicate alteration of the system from its original condition 
to another. Erasure (@, B, &c.) indicates disappearance 
of a system by resorption. Suffixes (A,, B,, &e.) indicate 
homologous systems in order of age or size. Kneclosure 
A 
, i ) indicates passage to a non-functional state. 
Plus sign (A+, B+, &e.) indicates increase of the system, 
