The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene . s subterraneandwellings on the banks: this is the well-known Duck-billed Platypus (Ornithorhynchus paradoxus): it is web-footed, has a thick, soft skin, and broad, flat jaws, whichvery much resemble a ducks bill (Figs. 195, 196). Theother form, the Porcupine Ant-eater (Echidna hystrix), muchresembles the Ant-eaters, in its mode of life, in the cha-racteristic form of its slender snout, and in the great lengthof its tongue; it is covered with prickles, and can roll itselfup into a ball like a he
The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene . s subterraneandwellings on the banks: this is the well-known Duck-billed Platypus (Ornithorhynchus paradoxus): it is web-footed, has a thick, soft skin, and broad, flat jaws, whichvery much resemble a ducks bill (Figs. 195, 196). Theother form, the Porcupine Ant-eater (Echidna hystrix), muchresembles the Ant-eaters, in its mode of life, in the cha-racteristic form of its slender snout, and in the great lengthof its tongue; it is covered with prickles, and can roll itselfup into a ball like a hedgehog. Neither of these extantBeaked Animals possesses true bony teeth, and, in thispoint, they resemble the Toothless Mammals (Edentata).The absence of teeth, together with other pecuKarities ofthe Ornithostomata, is probably the result of comparativelyrecent adaptation. Those extinct Cloacal Animals whichembraced the parent-forms of the whole Mammalian class,the Promammalia, must certainly have been provided witha developed set of teeth, inherited from Fishes.^^ Some 148 THE EVOLUTION OF Fig. 195.—The Duck-billed (Ornithorhynchus paradoxus).Fig. 196.—Skeleton of Platypus. POUCHED ANllVIALS. 149 small single molars, found in the uppermost strata ofthe Keuper formation in England and Wurtemberg, andwhich are the oldest known vertebrate remains, probablybelong to these primaeval Promammalia. These teeth, bytheir form, indicate species that lived on insects; the specieshas been called Microlestes antiquus. Teeth belonging toanother closely allied Primitive Mammal (Dromatheriumsilvestre) have recently been discovered in the NorthAmerican Trias. On the one hand, the still extant Beaked Animals, and, onthe other, the parent-forms of the Pouched Animals (Mar-supialia, or Didelphia), must be regarded as representingtwo distinct and divergent lines of descent from the Pro-mammalia. This second Mammalian sub-class is veryinteresting as a perfect link between the two
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