8 



true relative rank of their families can be determined in that way. 

 We need only compare, among true Carnivora, the Plantigrades, the 

 Digitigrades, and the web-footed Seals, with the transformation of the 

 limbs in the embryo of Cats and Dogs, to be satisfied that the order 

 in which these animals are arranged by CUVIER, does not agree with 

 their natural metamorphoses, and that the Plantigrades should rank 

 below the Digitigrades, nearer to the Seals, and the Digitigrades 

 highest ; and the affinity of the Ice-Bear to the Seals will further 

 sustain this statement. 



These remarks will, at the same time, show that no investigations 

 are at present more needed to improve our natural methods in clas- 

 sification, than a thorough study of young animals ; and that an ex- 

 tensive illustration of the young of all the principal representations 

 of the great natural groups in the Animal Kingdom, would, for the 

 present, contribute more to the advance of Zoology, than any amount 

 of description of new species. 



But these investigations of young animals should be made with a 

 full knowledge of their various relations, and with the view of ascer- 

 taining chiefly those Zoological peculiarities, which may illustrate 

 more fully the value of all these relations. 



There is another field of investigation hardly yet entered upon r 

 which is likely to contribute largely to the improvement of our 

 classification. I refer to the study of fossils, compared in their 

 structural peculiarities, with the embryos of their living representa- 

 tives. It has already been shown that many fossils of the earliest 

 geological periods have a close resemblance to embryonic forms of 

 the present day ; and that, in their respective families, these fossils 

 rank among the lower types. 



This result, in itself, should be a sufficient inducement to trace this 

 double relation, and to ascertain from as many fossils as possible, 

 whenever they are sufficiently well preserved to allow of such com- 

 parisons, what is the extent of their analogy to embryonic forms, of 

 the present period, and also, what is the amount of affinity they 

 have to the lower types of their respective classes. 



I w r ould mention in this connection, the necessity of a revised 

 comparison of the Trilobites, with the earliest stages of development 

 of Crustacea, when it will be found, as I have already seen it, that 

 almost all the genera of Trilobites seem to be the prophetic images, 

 in a gigantic form, of the different types the Crustacea present in 

 their embryonic state. The different degrees of development of 

 these different types, when contrasted with each other, will go far to 



