52 
eyes readily distinguish species one from another, 
and the males of many from the females. These 
discriminations act on the optics of the individuals 
of distinct species so as to produce peculiar excite- 
ment; doubtless barely analogous to any of which 
we are conscious; perhaps very different in every 
species of every genus and of every class. Were 
colours merely placed in a uniform plan, as for ex- 
ample, were each of the seven prismatic colours, 
with black, brown, and white, singly characteristic 
of any ten species, animal or vegetable, and their 
possible changes with relation to one another, as in 
stripes, ordained to designate other genera and spe- 
cies, the calculable changes of such stripes would 
exceed three millions. But the total known species 
of plants and animals do not exceed 300,000. But 
this methodised plan is characteristic of human 
operations: it has its calculable limit: not so the 
works of the Almighty; the stars of the milky 
way above us, and the dust of our summer foot- 
path, alike baffle our calculation. But the system 
of stripes or spots, however exact, would not afford 
that instantaneous indication of each object which 
is afforded by the distribution of external indices, 
which enable species to distinguish species, and males 
to know their mates, even individually. 
But the colours of nature are, indeed, not for- 
mally distributed in spots and squares and lines; 
but they are combined so as to exhibit the most 
elegant gradations, blending gently one with an- 
other, or contrasted so as to produce the most sur- 
