INTRODUCTION. 7 
modelled upon that of the adult, and where the scale of ideas is limited, 
they must be as essentially hereditary as the external form.* An English 
writer endeavors to found a distinction between instinct and reason, by 
citing the case of a young animal, as a monkey, being terrified by one of 
its natural enemies, as a large serpent, when seen for the first time, which 
would not be the case with a young human being. Nevertheless, if man 
were for ages subject to be devoured by a large reptile, watching and 
caution would at length become habitual, and be transmitted as an instinct. 
The brain of the young is not necessarily that of the adult, but that of the 
adult at an earlier stage. So a quality or habit is not always transmissible 
from a parent to its immediate offspring, but it may appear in a more 
distant descendant, by a kind of “alternation of generations.” Colonel 
Hamilton Smith considers the spotted horse as an original Asiatic race 
with which the ordinary breeds were sometimes crossed, and he thus 
accounts for the occasional appearance of examples of it. The original 
race is mild and intelligent, which is one reason for its frequent use in 
equestrian exhibitions. 
One of the most important inquiries in the history of animals and plants, 
is that which relates to their distribution. That of the latter has been 
treated of under Botany; and as regards animals, our contracted space 
limits us to the following general view. 
There are both aquatic and terrestrial animals, the number of which may 
perhaps be equal; but there are also species which can live both in water 
and on land, as many of the amphibia, and some other vertebrata. Some 
aquatic animals live partly in fresh, and some in salt water; but there are 
others which leave the sea to spawn in the fresh water, as the salmon. 
In the sea itself there are several regions depending upon the depth. Some 
marine animals live near or at the surface, others upon the bottom, in some 
cases within certain limits as to depth. Many land and sea animals live 
only as parasites upon or within others. Some species have a peculiar 
parasite, while others support several kinds. 
Zoogeography, or the geographical distribution of animals, teaches the 
circumstances and positions under which animals occur, both as regards 
individual species, genera, or larger groups. The chief circumstances 
which seem to contro] animal distribution, are temperature, elevation, and 
natural barriers ; whence it results that not only the continents, but much 
smaller regions, have their peculiar fauna. In proceeding from the tropics, 
species will be found to diminish rapidly. Some animals are circumscribed 
within very narrow limits, being confined to a single locality, as the curious 
reptile genus Amblyrhynchus to the Galapagos islands, or the Aurochs 
(Bison priscus) to a single forest in Russia. The genus Bradypus (sloth) 
and Dasypus (armadillo), Auchenia (llama), are confined to South America; 
the Marsupialia (possum, &c.) to America and Australia, and the Zebras to 
Africa. Others are more widely spread, as the dogs, bats, mice, We. 
* These views are favorable to the doctrine of innate ideas, which is generally opposed by 
speculative reasoners. 
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