THE DOCTRINE OF FINAL CAUSES. 511. 



for the most cautious man never to have recourse 

 to them in his explanations." After the survey 

 which we have had to take of the history of physio- 

 logy, we cannot but see that the assumption of final 

 causes in this branch of science is so far from 

 being sterile, that it has had a large share in every 

 discovery which is included in the existing mass of 

 real knowledge. The use of every organ has been 

 discovered by starting from the assumption that it 

 must have some use. The doctrine of the circula- 

 tion of the blood was, as we have seen, clearly and 

 professedly due to the persuasion of a purpose in 

 the circulatory apparatus. The study of compara- 

 tive anatomy is the study of the adaption of animal 

 structures to their purposes. And we shall soon 

 have to show that this conception of final causes 

 has, in our own times, been so far from barren, that 

 it has, in the hands of Cuvier and others, enabled us 

 to become intimately acquainted with vast depart- 

 ments of zoology to which we have no other mode 

 of access. It has placed before us in a complete 

 state, animals, of which, for thousands of years, only 

 a few fragments have existed, and which differ 

 widely from all existing animals ; and it has given 

 birth, or at least has given the greatest part of 

 its importance and interest, to a science which 

 forms one of the brightest parts of the modern 

 progress of knowledge. It is, therefore, very far 

 from being a vague and empty assertion, when we 

 say that final causes are a real and indestructible 

 element in zoological philosophy; and that the 



