270 



On the Classification of Animals 



Insectivores of the Microsthenes, and not through the higher 

 Carnivores or even any of the Megasthenes. 



The classes of Reptiles and Fishes may appear to be an excep- 

 tion. But the Perennih^'anchs (or the species with permanent 

 gills) among Ampliibians, if referred to the type of Fishes, and 

 especially to the Ganoid type, would rank low, as is obvious from 

 tbeir exsert and loosely-hung gills without gill-covers, the absence 

 of scales, and the general inferiority in- all structural arrange- 

 ments. The Ganoceplis, known only as fossils, and generally 

 regarded as Perennibranch Amphibians, have, it is true, a higher 

 grade of organisation, botb as regards gills and scales, being 

 allied in these respects to the highest of Ganoids. And this fact, 

 in view of the above canon, sustains the opinion, of Agassiz, that 

 the Ganocephs (or Archegosaurs) are actually Ganoids — having 

 a Eeptilian feature in the partial elongation of the limbs, but in 

 little that is fundamental in tlie structure beyond what belongs 

 essentially to the Ganoid-type. 



VII. The lines of gradation between classes, orders, and tribes, 

 are only approximating, not connecting, lines, there being often 

 wide blanks of the most fundamental character. The Ornitho- 

 rhynchus, although Duck-like in some points, leaves still a very 

 wide unfilled gap between the Mammal and Bird, and the Mar- 

 supials a still wider. The species are fundamentally Mammalian, 

 and Bird-like only in points of secondary importance. In a 

 similar manner, tliere are long blanks between the Obtocoids and 

 higher Mammals ; between Myriapods and either Insects or 

 Spiders ; between Beptiles and Mammals. The intermediate 

 groups belong decidedly to one or the other of the two approxi- 

 mating groups, and are never strictly intermediate. 



VIII. Under any class^ order, or trihe^ the lines of gradation 

 run in most cases between the degradational subdivision and 

 severally tlie gammatypic and hetatypic subdivisions, and far less 

 clearly, or not at all, between the gammatypic and betatypic 

 themselves ; that is, between J) and and D and /3, rather than 

 /S and y. For example, in the class of Mammals, the lines run 

 between Obtocoids and either Megasthenes or Microsthenes, and 

 not distinctly betvv^een Megasthenes and Microsthenes ; in Insec- 

 teans, between Myriapods and either Insects or Spiders, and not 

 distinctly between Insects and Spiders ; In Crustaceans, between 

 Entomostracans and either Decapods or Tetradecapods, and not 

 distinctly between Decapods and Tetradecapods, &c. There are 

 exceptions to the canon ; and still it is a general truth. 



IX. Under any class or order, the line of gradation between 

 the degradational and the hetatypic subdivision (or D and /3) is 

 often more distinct than that between the degradational and 



