1,58 Dr. Clarke's Description of an extraordinary 
seem peculiarly likely to assist in the prosecution of physiolo- 
gical researches. 
If we were never to see an animal except in its perfect 
state, we could form no just idea of the comparative necessity 
of the different parts. So also, if we were to attend alone to 
the complete structure which obtains in the more perfeckani- 
mals, we might be led falsely to conclude, that the usual 
connexion of parts, which we find in them, was essential to 
the structure and composition of animal matter. Of these 
parts, the brain and nerves, the stomach and digestive organs 
generally, the heart, and the lungs, would appear to be of 
such importance in the machine, that one would be induced 
to imagine that the functions of life could not be carried on 
without them : but in tracing the works of nature down- 
wards, we shall at length find animals gradually becoming 
more and more simple in their construction. The brain and 
nervous system are altogether wanting in some, and there 
are others which have neither heart nor lungs ; yet they 
continue to exist, and are capable of performing the most im- 
portant functions of animals. Thus the formation of one 
animal serves to throw light upon the economy of others. 
This great simplicity of structure is found, however, 
chiefly in animals the texture of whose bodies is nearly ho- 
mogeneous ; not consisting, as in more perfect animals, of 
parts so different from each other, as skin, intestines, &c. are 
from bone. 
It might therefore still be supposed, that all the compli- 
cated mechanism, found in the more perfect animals, is 
essential to the construction of such heterogeneous sub- 
stances, as those of which they consist. 
