Again, those remarkable scaly ant-eaters of the Old World--the pangolins (Manis)--stand alone amongst mammals as regards their dermal covering; having been classed {175} with lizards by early naturalists on account of their clothing of scales, yet their mouth is like that of the hairy ant-eaters of the New World.

On the other hand, the duck-billed platypus of Australia (Ornithorhynchus) is the only mammal which has teeth formed of horn, yet its furry coat is normal and ordinary.

Again, the Dugong and Manatee are dermally alike, yet extremely different as regards the structure and number of their teeth.

The porcupine also, in spite of its enormous armature of quills, is furnished with as good a supply of teeth as are the hairy members of the same family, but not with a better one; and in spite of the deficiency of teeth in the hairless dogs, no converse redundancy of teeth has, it is believed, been remarked in Angora cats and rabbits.

To say the least, then, this law {176} of correlation presents numerous and remarkable exceptions.
[Illustration: DUGONG.] To return, however, to the subject of homological relations: it is surely inconceivable that indefinite variation with survival of the fittest can ever have built up these serial, bilateral, and vertical homologies, without the action of some special innate power or tendency so to build up, possessed by the organism itself in each case.