69 



of this group have become greatly specialised in accordance 

 with their habits of life. Many extinct forms are known 

 from their fossil remains, and it is probable that the 

 Edentata were once a much larger groap than they are 

 now. They probably divided at an early period into several 

 distinct branches, the representatives of some of which {e.g., 

 Manis and Orycteropus) are very different from the other 

 members of the group. The existing Edentata ought pro- 

 bably to be considered as having degenerated somewhat. 



The Sirenia are probably the remains of a degenerate off- 

 shoot from the older Eutheria above the point of origin of 

 the Edentata. They are not closely related to any of the 

 higher groups of Mammals, and, therefore, probably diverged 

 before the Eutherian stem began to split up. In the Sirenia 

 the hind limbs are wanting, hair is almost entirely absent 

 from the skin, and the body is modified to suit the aquatic 

 habits of the animals. 



The remaining groups of the Eutheria are all more or 

 less closely allied to one another, but it is very difficult to 

 determine the lines of their evolution. As they can be 

 nearly all traced back to a generalised form, with characters 

 which may have been common to the ancestral Ungulata, 

 Carnivora, and Prosimise, the probability is that the main 

 stem split up soon after the separation of the primitive 

 Sirenia, into various branches leading to the main groups of 

 higher Mammals. These may be arranged in two series, the 

 one consisting of the ancestral Ungulata, from which probably 

 the Cetacea, Hyracoidea, Proboscidea and Kodentia arose at 

 different points in the series; and the other comprising 

 the common ancestors of the Carnivora, lusectivora and 

 Cheiroptera, and of the Prosimi® and Primates. 



The former of these two series is shown in the table 

 as diverging to the left and leading upwards through a long 

 series of ancestral Ungulata. The Cetacea probably arose 



