i 



XX.] COMPARATIVE MORPHOLOGY. 247 



could not be an ultimate law, but was one of which an 

 explanation ought to be sought. Just so, the law of pre- Exceptions 

 determined plan in morphology proves to be subject to ex- '^ P ^■^" 

 ceptions. I will mention one very remarkable instance. 

 Nearly all the Mammalia have seven vertebrae in the neck, Cervical 

 whether it is as long as in the giraffe, or as short as in the Mammalia. 

 whale. The only known exceptions to this are among the 

 various species of sloth and of manati ; and these two 

 families, it is to be observed, belong to orders that have 

 little else in common. In the manati genus, the usual 

 number of cervical vertebrae is six : in the Bracliypus 

 genus of sloths, it varies from eight to ten : but in the 

 Cholccpus Hofmanni, a species of sloth lately described 

 by Professor Peters, it is only six.^ Such an exception as 

 this, in my opinion, goes very far to prove that the law of 

 homology, or the law of adherence to types, is not an ulti- 

 mate law, but one which is in its own nature capable of 

 being explained by resolving it into simpler laws ; even 

 though the facts should prove to be too inaccessible, or too 

 complex, to admit of its being so resolved by any science 

 possible to man. 



Such is the relation between the law of Homology and 

 the law of Adaptation ; so wonderful is the adherence to 

 the minutest details of a type, while at the same time it is 

 modified so as to make it perfectly adapted to the most 

 different purposes (as in the case of the man's hand, the 

 dog's foot, the bat's wing, and the whale's paddle) ; that it 

 seems as if an intelligent power were adapting materials Intelligent 

 given to it by an unintelligent one. And this, I believe, is teiiirvent " 

 no mere illustration, but the actual fact. The Intelligent poweis. 

 Power is that creative intelligence which, as I have already 

 stated, I believe to direct the process of organic formation. 

 The Unintelligent Power is the power of hereditary habit. 

 I believe in the descent of all organisms from a few 

 germs ; I am still more strongly convinced of the descent 

 of aU organisms of the same type from the same ancestor ; 

 and as the vertebrate type is a very definitely marked one, 

 I am fully convinced of the origin of all Vertebrates from a 



^ Quarterly Journal of Science, April 1865. 



