. A manual of zoology. Zoology. 632 CHORD AT A. EcHiDNiD^, The spiny aut-eaters have the body covered with bristles, snout with a wonn-shaped tongue used iii catching insects; Echidna acideala of Australia, feet five-toed, with digging claws; ProecJiidua (Acantlioglossus) of New Guinea, three-toed. Ornithorhynchid^. The duckbills are toothless, close-haired animals witli lioruy jaws which resemble those of a duck; the flve-toed feet with a swimming web especially well developed on the fore feet. Ornithorhynelius paradoxus of m- Fig. —Ornithorhynelius paradoxus^ duckbill- (From
. A manual of zoology. Zoology. 632 CHORD AT A. EcHiDNiD^, The spiny aut-eaters have the body covered with bristles, snout with a wonn-shaped tongue used iii catching insects; Echidna acideala of Australia, feet five-toed, with digging claws; ProecJiidua (Acantlioglossus) of New Guinea, three-toed. Ornithorhynchid^. The duckbills are toothless, close-haired animals witli lioruy jaws which resemble those of a duck; the flve-toed feet with a swimming web especially well developed on the fore feet. Ornithorhynelius paradoxus of m- Fig. —Ornithorhynelius paradoxus^ duckbill- (From Schmarda.) The male has a spine with a gland on the hind feet which fits in a corre- sponding pit on the thigh of the female and apparently plays a role in copulation. The oldest fossil mammals are possibly to be regarded as belonging to the monotremes. These appear in the trias and form a group, MULTITU- BEECULATA (Allotheria), which is but imperfectly known {Trityhxion, Microlestes, Plagiaulax). Their multitubercular teeth resemble the tempo- rary ones of OrnithorhyivJuts, while there are indications that the cora- coid existed as a distinct bone. Less certain are the Protodonta (Broma- therium, Microconodon) of the American Jurassic, of which only the lower jaws are known. Sui Class IT. JfarsKpialia {DideJphin). These, like the remaining mammals, are viviparous. They have small eggs which undergo a total segmentation in most species, and developi in the maternal uterus, being nottrished by a secre- tion from its walls. In a few species there is a placenta which, in Peranu'lcs, is allantoic in origin, in l>asi/nri(S I'ivcrri/uis possibly also from the yolk sac. In most species there is no jilacenta. In all there is insufficient nourishment and the young are born in a very immature condition. They are therefore carried a long time by the mother in the marsuiiium, a j^ouch formed by a fold of skin on the posterior ventral surface, into which the nipi)les open. The ventral
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