188 Mr. H.E. Strickland on the Natural System 
cations of structure which constitute the characters of groups 
were given solely with reference to the external circumstances 
in which the creature is destined to live, it follows that the 
irregularities of the external world must be impressed upon 
the groups of animals and of plants which inhabit it. The 
supply of organic beings is exactly proportioned to the de- 
mand; and Nature does not, for the sake of producing a re- 
gular classification, go out of her way to create beings where 
they are not wanted, or where they could not subsist. Thus, 
for instance, the warm climate and varied soil of the tropics 
admits of the growth of a vast variety of flowers and fruits. 
The group of Humming-birds which feed on the former, and 
of Parrots which feed on the latter, are accordingly found to 
be developed in a vast variety of generic and specific forms ; 
while the family of Gulls which seek their food in the mono- 
tonous and thinly inhabited regions of the north, are few in 
species and still fewer in genera. Again, the variety of plants 
in the tropics admits the existence of a great variety of in- 
sects, and the family of Woodpeckers is proportionately nu- 
merous; while the Oxpecker (Buphaga), which seems to form 
a group fully equivalent in value to the Woodpeckers, is 
limited to but one or two species, because its food is confined 
to a few species of insects which only infest the backs of 
oxen. 
It follows, then, that the groups of organized beings will be 
great or small, and the series of affinities will be broken or 
continuous, solely as the variations of external circumstances 
admit of their existence, and not according to any rule of 
classification. If, indeed, we were to imagine a world laid 
out with the regularity of a Chinese garden, in which a cer- 
tain number of islands agreeing in size, shape, soil, and form 
of surface, were placed at exactly equal distances on both 
sides of the equator, we might then conceive the possibility 
of a perfect symmetry in the groups of beings which inhabit 
them ; but without some such supposition, I do not see how 
a class of animals or plants can be symmetrical in themselves, 
and yet be expressly adapted for conditions of existence which 
are eminently irregular. 
3. To pass from syllogism to induction, it 1s most certainly 
not the case that any definite number or geometrical property 
runs through the animal or vegetable kingdom. I do not 
wish on the present occasion to enter on any criticism of in- 
dividual systems, but it would be easy to show that no sym- 
metrical system yet proposed is a true picture of the real 
series of affinities. Without referring to the numerous gaps 
in these systems which are referred by their authors to species 
