174 EUTHERIA 



divisions which are called " orders." In the main zoologists 

 are now of accord as to the general number and limits of these 

 divisions among the existing forms, but the affinities and relation- 

 ships of the orders to one another are far from being understood, and 

 there are very many extinct forms already discovered which do not 

 fit at all satisfactorily into any of the orders as commonly defined. 



Commencing with the most easily distinguished, we may first 

 separate a group called Edentata, composed of several very distinct 

 forms, the Sloths, Anteaters, and Armadillos, which under great 

 modifications of characters of limbs and digestive organs, as well as 

 habits of life, have just enough in common to make it probable that 

 they are the very specialised survivors of an ancient group, most 

 of the members of which are extinct, although the researches of 

 palaeontology have not yet revealed them to us. The characters of 

 their cerebral, dental, and in many cases of their reproductive organs 

 show an inferior grade of organisation to that of the generality of 

 the subclass. The next order, about the limits of which there is no 

 difficulty, is the Sirenia, — aquatic vegetable-eating animals, with 

 complete absence of hind limbs, and low cerebral organisation, — 

 represented in our present state of knowledge by but two existing 

 genera, the Dugongs and Manatees, and by a few extinct forms, 

 which, though approaching a more generalised mammalian type, 

 show no special characters allying them to any of the other orders. 

 Another equally well-marked and equally isolated, though far mure 

 numerously represented and diversified order, is that of the Cetacea, 

 composed of the various forms of Whales, Dolphins, and Porpoises. 

 In aquatic habits, external fish-like form, and absence of hind limbs, 

 they resemble the last, though in all other characters they are 

 as widely removed as are any two orders among the Eutheria. 



All the remaining orders are more nearly allied together, the 

 steps by which they have become modified from one general 

 type being in most cases not difficult to realise. Their dentition 

 especially, however diversified in detail, always responds to the 

 formula already alluded to, and, although the existing forms are 

 broken up into groups in most cases easy of definition, the discoveries 

 already made in palaeontology have in great measure filled up the 

 gaps between them. 



Very isolated among existing Eutheria are the two species of 

 Elephant constituting the group called Proboscidea. These, however, 

 are now known to be the survivors of a large series of similar animals, 

 Mammoths, Mastodons, and Dinotheres, which as Ave pass backwards 

 in time gradually assume a more ordinary or generalised type ; and 

 the interval which was lately supposed to exist between even these 

 and the rest of the class is partially bridged over by the discovery 

 in American Eocene and early Miocene formations of the gigantic 

 Dinocerata, evidently offshoots of the great group of hoofed animals, 



