400 ZOOLOGY. 



between these and the universal primaeval life of the organic 

 world of this globe. 



" In selecting the natural family of the Salmonidae as a subject 

 of research, I have been guided by several considerations : I had 

 already made them the subject of extended research, and their 

 external characters offered favourable points of view for such an 

 inquiry. It is chiefly to the exterior that I give my attention in 

 the present Memoirs ; the interior will follow. I commenced 

 with the dentition, that natural -history character to which all, 

 whether naturalists or anatomists, ascribe such importance ; next 

 followed a brief inquiry into the systems of coloration and propor- 

 tion. To all these the transcendental applies, or ought to apply, 

 if true. That it is true as a theory I have not a doubt myself, 

 however I may fail in proving it to the satisfaction of others. 

 My immediate object is to prove the existence of a generic animal, 

 the product, no doubt, of hereditary descent from a species, but 

 in itself including the characteristics of all the species 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 commingling 

 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 ultimate 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 philo- 

 sophy which the theory of successive 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 transcen- 

 dental anatomy of the skeleton ; in the history of the branchial 

 arches we have the refutation of the * arrest of development' 

 theory ; in the external characters of the young salmon we have 

 the proofs that in the young of any of the family of the salmonidae 

 we may find the types of all the adult speeies 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 distinctly, specialisations recalling the antique 

 forms of animals which have long ceased to be. In the meta- 

 morphosis of the young salmon, the fins have at first forms which 

 belong to extinct species ; next a dentition, so perfect, so com- 



