Why the Monotremata are formed into a Sub-order--The lowest of the Mammalian Class--THE PORCUPINE OR LONG-SPINED ECHIDNA--An Ant-eater, but not an Edentate--Its Correct Name--Description of the Animal--Habits and Disposition--Manner of Using the Tongue--Where it is Found--Anatomical Features: Skull, Brain, Marsupial Bones--The Young--Species of Van Diemen’s Land and New Guinea--THE WATER-MOLE, OR DUCK-BILLED PLATYPUS--The most Bird-like Mammal--Various Names--Description--Their Appearance and Movements in Water--Their Burrows--Habits of an Individual kept in Confinement--Used by Natives as Food--How they are Captured--The Young--A Family in Captivity--the Snout--Jaws--Teeth--Tongue--Fore and Hind Feet--Heel--Spur--The Shoulder Girdle--Breastbone--Concluding Remarks on the Sub-orders--Postscript on the Monotremes. THE PORCUPINE OR LONG-SPINED ECHIDNA. This animal is the first example of some Marsupial beasts which are separated into a sub-order, because, in addition to the marsupial bones, there are some internal points of construction which are more bird-and lizard-like than those of the Kangaroo tribes. It contains animals which are the lowest of the Mammalian class, and are found only in the Australian natural history province. The Porcupine Ant-eater, as its name implies, has somewhat the shape of a Hedgehog or Porcupine, and it is fond of burrowing with its peculiar limbs, as well as of eating Ants with the assistance of its long tongue. But its internal anatomy and the construction of the skeleton differ from those of the true Ant-eaters, which belong to the order Edentata. It was called Ant-eater by its first describer (Shaw) in 1792, but a few years afterwards it was decided to belong to the same group as an animal about to be described--the Duck-billed Platypus, or Water Mole--and Cuvier, whilst believing that they both belonged to a peculiar order, separated this false Ant-eater from the Water Mole as a species and genus. He called this Hedgehog-like creature Echidna, from the presence of a spur on the heel, which is perforated, and which was erroneously supposed to be poisonous, like the fang of a Viper (Ἔχιδνα). The correct name is the Long-spined Echidna, or the Porcupine Echidna (_Echidna hystrix_). [Illustration: PELVIC ARCH OF THE ECHIDNA. (_a_ _a_) Marsupial Bones.]