966 Influence of circumstances on the Actions of Animals. 
of some important circumstance acts to change the parts of these 
living bodies. While Ranunculus aquatilis is immersed in water 
its leaves are all finely divided and the divisions are capillary, but 
when the stems of this plant reach the surface of the water, the 
leaves which develop in air are enlarged, rounded and simply lobed. 
If some root of this plant succeeds in pushing itself into a soil 
only damp, without being covered by water, the stems are short, and 
none of the leaves are parted into capillary lobes; it is called the 
Ranunculus hederaceus, which botanists regard as a species when 
they encounter it. There is no doubt that, in regard to animals, 
important changes in the circumstances in which they are in the 
habit of living, produce changes likewise in their parts, but here 
the mutations are slower in being brought about than in vegetables, 
and in consequence are less evident to us, and their cause less 
recognisable. Among the circumstances which have so much power 
to modify the organs of living bodies, the most influential are, 
without doubt, the diversity of places which they inhabit; but 
besides these are many others which have considerable influence in 
the production of the results in question. It is known that different 
places change nature and quality on account of their position, of 
their constitution, and of their climate. This is easily observe 
in visiting different places distinguished by these particular qual- 
ities. Behold, then, one cause of variation of animals and of vege- 
tables which live in these diverse localities; but that which is not 
sufficiently known, and even what is generally refused credit, is 
that each locality itself changes in time, exposure, climate, nature 
and quality, though so slowly in comparison with our lifetimes that 
we attribute to it perfect stability. Now, in one and the other case, 
these changed localities change correspondingly the relations to 
living bodies which inhabit them, bringing to bear new influences 
on them, It is known that when there are extremes in these 
changes there are gradations which are intermediate, and which fill 
the interval. Consequently there are shades of difference, which 
distinguish what we call species. It is therefore evident that the 
entire surface of the globe shows, in its nature and in the situation 
of the materials which occupy different localities, a diversity of 
circumstances which is everywhere in relation with that of the 
forms and of the parts of animals, independent of peculiar diver- 
