Animals and the Elements in which they Line. 223 



and sometimes even a fin-like fold of the skin upon the back. 

 If it can be shewn that the Sirenidse are an aquatic type of 

 a larger group embracing Pachyderms, the direct relation of 

 their structure and mode of life will be at once obvious, since 

 SirenidaB are either marine or fluviatile, while true Pachy- 

 derms are terrestrial ; and should we not be justified in con- 

 sidering the sub-aquatic Hippopotamus as inferior to its 

 more terrestrial relatives of the genera Rhinoceros, Elephant, 

 and Horse? Are we not to consider the Ornithorynchus, 

 with its pulmate hind-legs and spur, as inferior to Echidna \ 

 Are not the palmate Rodentia inferior to the terrestrial and 

 arboreal types \ Are not the aquatic Shrews inferior to the 

 arboreal Insectivora? All these secondary questions will 

 receive, in future, due attention, and will no doubt be satis- 

 factorily settled. But there are families in which we can 

 already see our way, and arrive at precise conclusions. Among 

 carnivorous Mammalia we have three distinct types, the Pin- 

 nipoda or seals ; the Plantigrada or bears, and the Digiti- 

 grada, dogs and cats. Now, even if objections were raised 

 against the association of the Walrus with the common Seals, 

 there can be no doubt of the inferiority of the latter when 

 contrasted with Plantigrada and Digitigrada. Their short 

 fin-like legs, their clumsy body, in connection with their 

 aquatic marine life, assign them a lower position, and the 

 Plantigrada must be considered as intermediate between 

 them and the Digitigrada. Now, among Digitigrades, even 

 if we take isolated genera, we are led to assign to the species 

 with aquatic habits, an inferior position among their nearest 

 relatives. The Polar bear comes decidedly nearer the Seals 

 in all its habits, than any other species of that genus, and, on 

 that ground, should be considered as inferior to the terrestrial 

 species. Again, the others, with their palmate fingers, rank 

 lower than their terrestrial relatives ; and we may even find 

 that such considerations will hold good among the varieties 

 of one and the same species ; for we have varieties among 

 the Digitigrade dogs, in which the fingers are palmate, a 

 character which is derived from the imperfect development 

 of their legs, preserving throughout life their embryonic 

 form ; and these varieties among dogs are the most playful, 



