192 , LAKE SUPERIOR. 



to have some principle bj which to regulate the internal details of 

 the edifice. 



We may indeed form natural divisions simply from structural evi- 

 dence, bring together all fishes as they agree in the most important 

 details of their structure, and combine all reptiles into one class, not- 

 withstanding the extreme differences in their external form. We may 

 also recognize the true aflSnity of whales, and bring them together 

 with other Mammalia, notwithstanding their aquatic habits and their 

 fish-like * form ; we may even subdivide those classes into inferior 

 groups upon structural evidence, and thus introduce orders, like the 

 Quadrumana, Carnivora, Rodentia, Ruminantia, &c., &c., among 

 Mammalia. But we are at once at a loss how to determine the relative 

 value of those groups, and to find a scale for the natural arrange- 

 ment of further subdivisions. After having, for example, circum- 

 scribed the Carnivorous Mammalia into one natural family, how are 

 we to group the minor divisions like that of the swimming Carnivora, 

 the Plantigrada and the Digitigrada ; or, after circumscribing the 

 reptiles into natural groups like those of Chelonians, Saurians, 

 Ophidians and Batrachians, how shall we, for instance, arrange the 

 various types of Batrachians ? To those who have been familiar 

 with our proceedings in all these attempts, it must be evident that 

 the grouping of our subdivisions has been almost arbitrary and en- 

 tirely left to our decision without a regular guide. We have, it is 

 true, subdivided the Batrachians into the more fish-like forms which 

 preserve their gills and tails, or at least their tails ; and into another 

 group, containing those wliich undergo a complete metamorphosis ; but 

 it has not yet occurred to naturalists to take this metamorphosis as the 

 regulating principle of classification, to arrange genera according to 

 their agreement with certain degrees of development, in the natural 

 order of changes Avhich the higher of these animals undergo. Now 

 it is my firm belief, that such a new principle can be introduced into 

 our science ; that methodical arrangement may be carried into the most 

 minute details, without leaving any room for arbitrary decision. Pro- 

 teus, Menobranchus, Amphiuma, Triton, Salamandra will hereafter 

 have a natural place in our classification, which will be commanded 

 by embryology, and no longer be left to a vague feeling that aquatic 

 animals are lower than amphibious and terrestrial ones, and that the 



