ADDITIONS. 



so have we in like manner, for the purposes of General Homology, 

 to solve the Problem of the Signification of Limbs. The whole of the 

 animal being a string of vertebrae, what are arms and legs, hands and 

 paws, claws and fingers, wings and fins, and the like? This inquiry Mr. 

 Owen has pursued as a necessary part of his inquiries. In giving a pub- 

 lic lecture upon the subject in 1849, 4 he conceived that the phrase which 

 I have just employed would not be clearly apprehended by an English 

 Audience, and entitled his Discourse " On the Nature of Limbs :" and 

 in this discourse he explained the modifications by which the various 

 kinds of limbs are derived from their rudiments in an archetypal ske- 

 leton, that is, a mere series of vertebrae without head, arms, legs, 

 wings, or fins. 



Final Causes. 



It has been mentioned in the History that in the discussions which 

 took place concerning the Unity of Plan of animal structure, this prin- 

 ciple was in some measure put in opposition to the principle of Final 

 Causes : Morphology was opposed to Teleology. It is natural to ask 

 whether the recent study of Morphology has affected this antithesis. 



If there be advocates of Final Causes in Physiology who would push 

 their doctrines so far as to assert that every feature and every relation 

 .11 the structure of animals have a purpose discoverable by man, such 

 reasoners are liable to be perpetually thwarted and embarrassed by the 

 progress of anatomical knowledge ; for this progress often shows that 

 an arrangement which had been explained and admired with reference 

 to some purpose, exists also in cases where the purpose disappears ; 

 and again, that what had been noted as a special teleological arrange- 

 ment is the result of a general morphological law. Thus to take an 

 example given by Mr. Owen : that the ossification of the head originates 

 in several centres, and thus in its early stages admits of compression, 

 has been pointed out as a provision to facilitate the birth of viviparous 

 animals ; but our view of this provision is disturbed, when we find that 

 the same mode of the formation of the bony framework takes place in 

 animals which are born from an egg. And the number of points from 

 which ossification begins, depends in a wider sense on the general 

 homology of the animal frame, according to which each part :s com- 

 posed of a certain number of autogenous vertebral elements. In this 



4 On the Nature of Limbs, a discourse delivered at a Meeting of the Royal 

 Institution. 1849. 



