90 Incomplete Adaptation as illustrated [| February, 
Under the law of natural selection, the perfection of the character 
will ultimately be reached, but a very long period, to say the 
least, must elapse during which it is still incomplete. 
Again, the conditions surrounding a species are constantly 
changing, usually slowly, but sometimes rapidly or suddenly. In 
this way the usefulness of certain characters is frequently de- 
stroyed, but the species cannot lose the character; it persists and 
gradually becomes atrophied or transformed into a different one. 
Such changes in organisms are very slow, and vast periods are 
passed through before they are completed. 
Now, considering the changes going on at all times in the 
conditions under which species exist, it may often happen that 
the ‘period during which adaptation is incomplete from both 
these causes, is greater than that during which it is complete. 
Indeed, as a matter of fact, the adaptation is never absolutely — 
complete, the organism being always, as it were, behind its envi- 
ronment, as the tides are behind the moon. . 
If this be true, we ought to expect constantly to find examples 
of incomplete adaptation. A character which required to be 
complete before it could be advantageous could never be acquired 
by natural selection. All such characters as are acquired must 
be advantageous in proportion as they are complete. 
Naturalists must therefore learn to regard a large proportion of 
the characters which they find to exist, as partial or uncompleted 
characters, useful to the species in proportion as they are devel- 
oped, but capable of greater adaptation. 
There are, moreover, two general classes of characters with 
respect to their usefulness and advantageousness to the species. 
Those of one of these classes are only useful to a certain limited 
degree, beyond which they may be injurious, and which only ap- 
ply to particular species in their relations to definite existing con- 
ditions. Such characters may be called sfecial. 
The other class, which may be distinguished as general, apply 
to all organisms, and are less limited in their degrees of possible 
development. 
Passing over the class of special characters, I propose to illus- 
trate the principles above stated, by an example in the class of 
general characters taken from the vegetable kingdom. 
The distinction of sex is a condition advantageous to all plants, 
and one in the process of attaining which a large number of grada- 
