186 M. Agassi? on the Classification of Fishes, 



as an attempt is made to establish a complete system of natu- 

 ral affinities throughout the entire animal kingdom. The 

 lacunae are in fact too obvious and too numerous, when fossils 

 are not taken into account, to admit of zoologists for the future 

 dispensing with the enumeration of them along with the living 

 species, in their attempts at classification.* For, by omitting 

 them, we obtain only the fragments of the frame-work, and 

 can attain only to an incomplete exposition of the plan fol- 

 lowed in the creation of organized beings. We have long 

 been assured of the fact that the beings which have disappeared 

 fyom the surface of the globe, far from having lived simulta- 

 neously, succeeded each other at diff"erent epochs, and have be- 

 longed to diff'erent creations, or rather that they have consti- 

 tuted series by themselves which have had a limited existence, 

 and been replaced by others after longer or shorter intervals. 

 Hence arise new requirements for systematic zoology. It will 

 not be sufficient henceforward to group genera and species ac- 

 cording to their organic affinities ; we must also take into ac- 

 count the relative age of their appearance on the surface of 

 the globe, and the importance of each group in the different 

 epochs of the general development ; in a word, zoology oughjt 

 to comprehend in its systems the genealogy of the whole ani- 

 mal kingdom. 



Important works have already pointed out the relations 

 which exist between the natural affinities of the genera and 

 species of many families, as well as their geological age ; but 

 perhaps no class exists in which this succession of types, 

 and their relations with the geological formations to which they 

 belong, is more evident than among fishes. It may, indeed, be 

 affirmed, that the closest connection exists between the prin- 

 cipal types of this class, and the epoch of their progressive de- 

 velopment. We have only to glance at the tables of species 

 characteristic of the formations, which I published at the end 

 of vols. 2, 3, 4, and 5 of my work,t to be convinced that each 



* \n my monographs of living and fossil Echinodermes, I have en- 

 deavoured to realise in certain groups, still very few in number, it ia 

 true, this idea of a union of zoology with paleontology and comparative^ 

 anatomy. It is much to be wished that similar attempts were madQ 

 with reference to all the classes of the animal kingdom. 



I Recherches sur les Poissons par L'Agassiz. Qto, 



