DISTRIBUTION OF ORGANISMS. 193 



Mammalia they may at the best be called ; and which are 

 even nearer to the bird character than the three orders above 

 enumerated. These are the Monotremes and Marsupials ; 

 animals now almost restricted to Australia, but which were 

 formerly more widely distributed. In the brain and other 

 parts of the organization, they are decidedly bird-like. But 

 this is not all, for, in the only surviving monotremes, the 

 ornithorhynchus and echidna, we see the bill and web-feet of 

 the swimming-bird still unchanged, the former animal being 

 a semi-rodent, and the latter a semi-insectivore. Here is a 

 gradation most remarkable, the point reached being only, as 

 it were, half way towards the higher form of existence. It is 

 also very remarkable to find amongst the more numerous 

 marsupials, genera recalling the rodent and the insectivorous 

 forms, as if these were only further advances along similar 

 lines. 



Reverting to the genealogy of the higher orders of Mam- 

 malia, we find ourselves introduced by the cetiosaur and the 

 remark as to the osteology of the dugong, into the confines of 

 the Cetacea, the marine or fish-like order of their class. In 

 this group of animals, what first strikes us is that, while 

 united by a common medium of existence, and some pecu- 

 liarities fitted thereto, they are otherwise extremely various, 

 as much so indeed as all the land mammalia together. The 

 whale, the dolphin, the seal, are animals fully as different 

 from each other as the panther and the elephant, the deer and 

 monkey. Naturalists now begin to say that the Carnivora 

 (lions, bears, genets, shrews) are represented in the seals, and 

 the great pachyderms in the cetacea ; the ruminants, also, in 

 the herbivorous cetes (manatus and dugong). Obscure as is 

 our knowledge of the aquatic mammals, this relation is indu- 

 bitable, but its real character has never been read. It becomes 

 quite intelligible when we arrive at the idea of a genealogical 

 system ; but in no other way, to all appearance, can it be 

 explained. 



The aquatic mammals are not properly one distinct order, 

 nor two either. They merely form the initiatory stages of 



