MUTABILITY., 173 
more detail, processes are frequently abridged or totally 
omitted which once, while they were being acquired 
and after they had been established, occupied a longer 
period, but in the course of selection either became of 
less importance to the individual, or preserved a physio- 
logical value only as phases of transition. 
The second great class of characters, namely, those 
which have been newly acquired and depend on adap- 
tation, pre-suppose the mutability of the organism. 
This is a fundamental phenomenon of organic bodies. 
It is inherent in the minutest morphological constituents, 
in protoplasm, and in cells, and in the morphological ele- 
ments evolved from them, the pervading and determining 
individual life of which results in the collective life of 
the creature. The organic morphological element is 
in a staté of saturation; it is continually imbibing and 
emitting, and its stability is therefore constantly depen- 
dent on the supply of material for its functions. For 
nutrition, which generally and wholly determines the 
external appearance and the nature of the individual, is 
accomplished by the innumerable cells and their deriva- 
tives. Every fluctuation of supply in any part of the 
organism, nay, in any point in the surface of a microsco- 
pic reef-builder, must necessarily involve a modification of 
textural parts, or of integrated textural groups or organs, 
Mutability' is thus a character resulting from the 
intrinsic nature of organism, and dependent on external 
conditions which determine quantity and form, as 
well as the development and transformation of the 
elementary constituents, or their abortion and retro- 
gression. These effects may be exhibited in a polype- 
stem, which as a whole represents the individual, in its 
