37 
of the southern hemisphere ; and the commonly received notion that 
all animals in all points of their structure are completely adapted tc 
the external circumstances of their native habitat, must by no means 
be supposed to imply that in those parts of the earth "where the 
temperature is the same that the animals are the same ; the con¬ 
trary being notoriously the fact in the extreme case I have given of 
the temperate and cold latitudes of opposite hemispheres. 
I his leads us to the law of representative forms, or species, of ani¬ 
mals, which isnotonlyof the highest interest to the philosophical zoolo¬ 
gist, but has a direct influence on acclimatisation. It is found that 
those parts of the world having similar conditions of surface and 
climate, but separated by natural obstacles one from the other, are 
inhabited commonly not by the same animals, but by “ representa¬ 
tive species, so like them in size, shape, colour, and habits, that to 
the common eye they are frequently identical, while the zoologist can 
easily prove that they are really distinct specific creations, originally 
placed, probably as a single pair, in the middle of the district they 
inhabit, and which could not, owing to their specific distinctiveness, 
have beeu originally derived by breeding from those similar species 
of other similar parts of the world which they are said to represent. 
This fact of the existence of “specific centres” of creation, or the 
probable origin of all the individuals of each distinct species of 
animal from one first created pair set down in the centre of a dis¬ 
trict towards the circumference of which the gradually increasing 
progeny radiated, the species becoming gradually rarer as it ap¬ 
proached the boundary—this fact explains the appearance on the 
map before you of the native habitat of each well known useful 
animal there indicated being circumscribed by one irregular curved 
line, having but one centre. Now, as there are representative species 
of plants having similar properties for food in widely separated 
places of similar climatal and surface characters, as well as representa¬ 
tive species of animals; we find that all the external circumstances 
influencing the life or well-being of the different species represent¬ 
ing any given one, are the same for all, and we accordingly find that 
the acclimntiser may, as you would theoretically expect, bring with 
the absolute certainty of success all the representative species of any 
group into each of the localities. This is the first great principle 
involved in successful acclimatising, and is practically recognized, 
although the whole subject is so new that hitherto the natural laws 
on which success depend have scarcely been indicated. Kepresenta- 
tive forms are not confined to the simple eases I have mentioned of 
corresponding latitudesin different hemispheres; butwliile you find the 
t 
