116 MAMMALIAN DESCENT. [Llct. IV. 



worthy of mention. It is not nntil we are some good lieiglit in the 

 mammalian scale, that we find the mechanism of the ear perfected hy 

 what is called a stapes, or stirrup-bone, in the middle-ear, fitting on 

 to the vestibule of the inner or essential ear. The oviparous trihes 

 which have that peculiar operculum or covering to the oval opening 

 of the vestibule (fenestra ovalis), namely. Amphibia, Reptiles, and 

 Birds, nearly always have it stalked, so that it forms a httle column 

 (columella), with a dilated upper or iniier end. The Prototheria, and 

 several of the Metatheria, have this columella instead of the stapes or 

 stirrup-shaped element in the middle-ear ; in the Edentata the 

 Armadillos and the Aard-vark have a stapes ; the Sloths, whilst in 

 their embryonic state, the Ant-eaters, and the Pangohns, have a 

 columella. Thus, in this transitional condition between the oviparous 

 and nobler mammalian tribes, the Edentata and the Marsujiials are 

 about on an equality. And this is true all round ; for in some things 

 the latter have the pre-eminence, whilst in others the Edentata are 

 manifestly superior to the Opossums, Phalangers, and Kangaroos. 

 If the New World and the Old "World Edentata ever had common 

 parents, a considerable amount of time must have elapsed since, to 

 give them the chance of becoming so very distinct as we now find 

 them. If the long-tongued ant-eating Woodpecker is a kind of side 

 branch from the primary Passerine stock, and the long-tongued 

 insectivorous Chameleon is a sort of side-branch of the Lizard stock, 

 then we may expect curious things to take place in a mammal also, 

 which loses all his teeth tlirough taking to li'^'e on Ants. I 

 am arguing as my esteemed colleague Professor Elower argues, 

 and we are of one mind on this matter. I am also in agreement 

 with him when 1 incline to put the Aard-vark a good way off from 

 the rest of the Order ; it comes nearer the Insectivora than any 

 other member of the group, whilst the Pangolin refuses to acknow- 

 ledge more than general relationship with the forms from the New 

 Trojjics. 



Yet the Pangolin has an equal right with them to be considered a 

 descendant of some prototherian beast — some common ancestor to 

 him, to the Neotropical forms, to the Duck-billed Platypus, and to 

 the ant-eating spiny Echidna. 



All the better sort of Mammalia have a plate of bone dove-tailed 

 in between the great skull-bones (parietals) and the back wall of the 



