based on the principle of Cephalization. 333 
(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 Odtocoids, 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 
& 
tion, and some other Reptilian characteristics, are outside of 
The term hemitypic has been shown in the preceding paper to 
