82 
SYSTEM OF NATURE. 
It will be observed by those who take an interest in 
comparative anatomy, that the vertebrated animals are 
normally four-limbed. It is quite obvious that this chai’acter 
is not confined to the normal or central group which have 
so frequently been described as quadrupeds. The posses¬ 
sion of two pairs of jointed organs of locomotion is a 
character of vertebrated animals generally, and not a cha¬ 
racter confined to a single class. Amongst those which are 
called the lower vertebrated animals, we shall find that these 
organs of locomotion have undergone great modification. 
In some classes we find animals — as snakes, eels and lam¬ 
preys — in which scarcely a vestige of limbs remains : in 
the marsupials alone can they be said to maintain, with any 
stability, their normal employ of terrestrial progression : 
in birds their office appears to be equally divided be¬ 
tween the earth and air. Now in the invertebrated animals 
so great a change of structure has taken place, that all at¬ 
tempts to trace these four implements of locomotion must 
entirely fail. It has been said of plants that they are 
animals turned inside out: this definition strikes me as 
applicable to the invertebrate, when contrasted with the 
vertebrated groups ; the former may be characterised as 
inverted vertebrates. Hence we not only do not find, but 
cannot expect to find, any trace of similarity between the 
legs and wings of vertebrates and invertebrates ; the same is, 
in a great degree, the case with the organs of the senses. 
Sight, hearing, smell, taste, touch, and locomotion, were 
requisite for animals adapted for living on the earth, and 
their Almighty Creator has been pleased to supply these 
powers to animals constructed on a variety of plans : each 
province of animals had to live, feed, move, breathe and 
breed on the same earth, and therefore a degree of simi- 
