26 
the final cause cannot be substituted for the 
physical in physiology any more than in other 
sciences; and this is what was meant by the 
assertion of Bacon, that the doctrine of final 
causes is sterile. The object of physiology is 
to explain, not why, but how, the various func- 
tions of life are carried on. But when the laws 
of life are even partially ascertained, and their 
application understood, i. e. when physiolo- 
gical facts are referred to their physical causes, 
they afford many proofs of design and con- 
trivance, and so furnish a most important ad- 
dition to the general science of final causes. 
The science, relative to living bodies, which 
may truly be said to have its foundations laid in 
the study of final causes, is the science of Com- 
parative Anatomy, or of animal morphology; 
1. e. the exposition of the modifications which 
the general type of animal structure, and the 
plan of the functions carried on in that structure, 
undergo in the different classes of animals, and 
by means of which the objects of the animal cre- 
ation are accomplished by the laws of physio- 
logy throughout the whole extent of creation. 
These modifications are determined by the cir- 
cumstances in which animals are placed on the 
one hand, and by the purposes which they are 
to serve in the creation on the other. Every 
variation of structure has its use, in reference to 
one or other of these objects, and the branch of 
natural history which consists in the descrip- 
tion and arrangement of these varieties cannot 
be properly treated otherwise than by keeping 
their uses constantly in view. 
Thus, in regard to the function of digestion 
in the higher animals, its physiology, properly 
speaking, consists in reference to the laws of 
sensation, of instinct, of muscular motion, of 
secretion, as modified by changes in the condi- 
tion of the nervous system, of absorption, and 
of vital affinities and assimilation so far as 
they are known, by which the reception of 
aliment, and the changes on the aliment re- 
ceived into the body are effected; in this en- 
quiry our object is explanation, and however 
useful the observation of the purpose served by 
the organs of digestion may be, in suggesting 
enquiries or experiments by which the laws of 
which we are in quest may be made out, it is 
an interruption, not an assistance, to refer to 
these purposes, or to the importance of the 
function in the animal economy, as if we thus 
obtained an explanation of the phenomena : 
but when these different laws of vital action 
are explained, their adaptation to the object in 
view is properly stated as a branch of the doc- 
trine of final causes. And when we trace the 
modifications which the organs and function of 
digestion undergo in the different tribes of ani- 
mals, in the carnivorous, the herbivorous, and 
the graminivorous,—in the quadruped, the 
bird, the fish, the insect, the polype, &c., and 
compare these with the provisions for assimila- 
tion and nutrition in vegetables, our object 
is merely description, and the arrangement by 
which we must be guided in this department of 
natural history is clearly laid down by atten- 
tion to the purposes which these modifications 
are ipunded to serve, as adapted to the circum- 
INSTINCT. 
stances and to the offices of animals, i.e. to 
their final causes. : al 
As, in this science of morphology, or 
tracing the varieties of “ metamorphosed sym- 
metry,” we do not seek to assign the physics 
causes of any phenomena, it is no abuse of the 
doctrine of final causes to assume it as the 
basis of our arrangements; and that the prin. 
ciple of the unity of plan in the animal ere 
tion, without the study of the conditions o 
existence of the different tribes of animals, by 
which it is modified, and of the instincts ac 
companying each modification, is truly steri 
was clearly shewn by Cuvier, and has 
ably illustrated by Mr. Whewell.* ; 
is observation is strictly applicable to the 
instincts of animals, considered as an essenti 
element in their physiology. We obtain no 
explanation of the phenomena of instinet by 
referring to their use, or final cause; but th 
inferences drawn from the study of instine 
as to the existence and attributes of the 
Author of the universe, and the insight 
thus acquire into the arrangements of the 
animal creation, are not, on that account, the 
less certain or the less important. ‘ 
In order to perceive the extent and impor 
ance of these inferences, it is necessary to co 
sider, as has been stated above, not only the 
mutual adaptation of structure and instincts 
each other, but also the adaptation of both, 
the case of every animal, first, to the purpe 
of its own economy, and secondly, to the 
purposes which it is fitted to serve in the 
general economy of nature. ra 
Assuming, as we may safely do, that one 
great object, if not the most essential object, 
of all the arrangements of organized beings i 
to secure the greatest possible amount of sen- 
tient enjoyment throughout the world, the 
varying instincts and powers by which animals” 
provide themselves with food will appear on 
consideration to be better adapted to the attain- 
ment of this end than they could have been on — 
any other plan, consistently with the general 
laws, that animal enjoyment depends on the 
maintenance of organized animal structure, and 
this on the continual appropriation and assimi- 
lation of previously organized matter. The 
different races of animals are widely diffused 
over the globe by the powers which ae De 
granted them of indefinite reproduction. Those 
of them which are immediately dependent on 
vegetables for subsistence are naturally limited 
by the extent of surface over which v i 
is spread ; and when this limit has been at-— 
tained, the only expedient that can increase the 
number of animals (and it may be added, one 
which at the same time varies and multiplies — 
the kinds of animal enjoyments) is to make 
animals prey on one another, either in the 
living or dead state. “ Such is the command 
given,” says Dr. Roget, “ to countless hosts 
of living beings which people the vast 
of ocean ; to unnumbered tribes ofinsects which — 
every spot of earth discloses; to the greater — 
number of the feathered race, and also to a 
ye 
* Ib. p. 472, et seq. , 
