364 ZOOLOGY. 



applies, or ought to apply, if true. That it is true as a 

 theory J have not a doubt myself, however I may fail in 

 proving it to the satisfaction of others. My immediate o'< 

 is to prove the existence of a generic animal, the product, no 

 doubt, of hereditary descent from a species, but in itself in- 

 cluding the characteristics of all the s]rics belonging to that 

 natural family; or, in other terms, proving hereditary descent 

 to have a relation primarily to genus or natural family. By 

 this term I endeavour to explain family likenesses com- 

 mingling with the generic ; the greater or less resemblance, 

 for example, of an individual with other affiliated races, to none 

 of which it belongs by strict hereditary descent. My ulti- 

 mate aim is to offer a scientific explanation of the appearance, 

 from time to time, of seemingly new species on the earth, 

 and of the extinction of others, thus restoring to legitimate 

 science that branch of philosophy which the theory of suc- 

 cessive creations, invented by Cuvier and still maintained by 

 his followers, had clearly removed from it. To prove the 

 unity of the organization, the unity of creation, and the serial 

 unity of all that lives or has ever lived, forms the aim of the 

 first part of this inquiry. 



" Probably no class of animals presents so many subjects for 

 deep contemplation to the philosophic naturalist as the class 

 fishes. They have furnished the chief materials for the tran- 

 scendental anatomy of the skeleton ; in the history of the 

 branchial arches we have the refutation of the ' arrest of de- 

 velopment' theory ; in the external characters of the young 

 salmon we have the proofs that in the young of any of the 

 family of the salmonidse we may find the types of all the adult 

 species of the family, thus rendering doubtful the theory of 

 the transmutation of species, and offering the only probable 

 solution of the most difficult of all questions the appearance 

 of new species and even genera on the surface of the globe. 

 Lastly, it is in the same class, fishes, that we find most dis- 

 tinctly, specialisations recalling the antique forms of animals 

 which have long ceased to be. In the metamorphosis of the 

 young salmon, the fins have at first forms which belong to 

 extinct species ; next a dentition, so perfect, so complete, as 

 to embrace the adult formulae of all existing species of the 

 family, so that to convert the dentition of one species into 

 another, nothing is ever added, but merely a something left 

 out. Contrary, then, to the theories of those who maintain 

 that the adult alone is perfect, we find that it is the young 



