116 MAMMALIAN DESCENT. [Lect. IV. 



worthy of mention. It is not until we are some good height in the 

 mammahan scale, that we find the mechanism of the ear perfected by 

 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 tribes 

 which have that peculiar operculum or covering to the oval opening 

 of the vestibule (^fenestra ovaJis), namely, Amphibia, Eeptiles, and 

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

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

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

 stirru]3-shaped element in the middle-ear ; in the Edentata the 

 Armadillos and the Aard-vark have a staj^es ; the Sloths, whilst in 

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

 columella. Thus, in this transitional condition between the oviparous 

 and nobler mammalian tribes, the Edentata and the Marsupials are 

 about on an equalit}'. 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 ISJ^ew "World and the Old "World Edentata ever had common 

 l^arents, 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 kmd 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 through taking to live 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 I 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 grouj^, whilst the Pangolin refuses to acknow- 

 ledge more than general relationshi]) with the forms from the Il^ew 

 Tropics. 



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

 descendant of some i)rototherian beast — some common ancestor to 

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

 the ant-eating spiny Echidna. 



All the better sort of jSIammalia have a j)late of bone dove-tailed 

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



