based on the Principle of Cephalization. 



95 



for terrestrial life are in the type-idea. Fishes are therefore 

 outside of type-limits, or are degradational species. 



The Mammal-type, the highest under Vertebrates, in addition 

 to the characteristics of the Vertebrate type, has that of being 

 viviparous in its births, embracing under this quality that of sus- 

 taining the embryo by placental nutrition until its maturity (as is 

 not true of the oviparous) ; and with this there is also that of 

 sustaining the young for a while after birth, by suckling. Hence 

 the Ootocoids, in which there is only imperfect placental nutrition, 

 and birth is premature, and there is an approximation thus to 

 oviparous species, constitute a degradational type. 



The Megasthene-type, under Mammals, has its degradational 

 group in the Cetaceans or Mutilates, which fail mostly of limbs, 

 and are aquatic species ; and the Carnivore, its degradational 

 group in the Seal and related Pinnipeds. The latter have the 

 type-structure of the Carnivores, while the Mutilates have the 

 type-structure of neither Carnivores nor Herbivores, and are there- 

 fore an independent type under the division of Megasthenes. 



Again, the Bird-type, in addition to the characteristics of the 

 Vertebrate-type, embraces features adapting the animal to flying, 

 as feathers and wings ; perfect circulation ; and also a vertebral 

 column which is posteriorly limitate, instead of one admitting of 

 a caudal elongation — -somewhat as Insects and Spiders are closed 

 types behind, in contrast with the multipUcate Myriapods. Hence 

 the Keptilian Birds, having indefinite posterior elongation, and 

 some other Beptilian characteristics, are outside of type-limits. 

 So, again, imder the subdivisions of Birds, species that have the 

 wings unfledged or but half-fledged, and which, therefore, cannot 

 lead an aerial life, are degradational ; and species that have the 

 feet imperfectly digitate by their being web-footed, and which 

 therefore lead a semi-aquatic life, are semi-degradational in the 

 group to which they may belong. 



These examples are sufficient to illustrate the uses of the words 

 typical and degradational. 



It is of the highest importance, for the correct classification of 

 species, that in all cases it should be rightly determined whether 

 a degradational genus is degradational to the/aim7j/to which it be- 

 longs, or to the tribe or order, or to a still higher division. Al- 

 though Seals and Whales are similarly adapted to the water, it is 

 plain to one familiar with the species that the former are degrada- 

 tional Carnivores, and the latter degradational Megasthenes, as 

 stated above. But like cases come up in every part of the Animal 

 Kingdom, and close study is necessary for a true decision. The 

 first preliminary towards such a decision is a clear idea of the 

 class-type, order- type, tribe- type, or subordinate type under which 

 the genus or group falls. 



