Fig. 53.—Brain of Echidna aculeata, dorsal view. (Nat. size.) (From Parker and Haswell's Zoology.)
Fam. 1. Echidnidae.—This family contains two genera, of which Echidna is the older and much the better known. The skin is abundantly covered with spines, with which are mingled hairs. The snout is tapering, the tail rudimentary, and the fingers and toes five in number. The spur and gland upon the calcaneum are smaller than in Ornithorhynchus. The claws are very strong, serving to tear open the ants' nests, upon the inhabitants of which the Echidna feeds, licking them up with a long extensile tongue like that of Myrmecophaga. In relation to this habit the salivary glands are enormously developed, and indeed the animal has been confounded with Myrmecophaga,[[57]] as the vernacular name "Australian Anteater" exemplifies.
In the skull the Echidna differs from Ornithorhynchus in the greater extension backwards of the palatines, and the larger size of the pterygoids. The extent and relations of these bones to each other is not at all unlike that which obtains in many Whales. The premaxillae show traces of the same divergence followed by convergence of their ends that is seen in the Platypus. There are only sixteen pairs of ribs, and either three or four lumbar vertebrae. Echidna has no trace of teeth, and there are no horny pads which take their place; the mouth is as edentulous as in the true American Anteaters. The brain (Fig. 53) is marked by sulci, contrary to what we find in Ornithorhynchus. The genus has been divided into three species, but it is doubtful whether more than one can be allowed, which ranges from Australia through the Papuan region. While there is but one species of true Echidna, a New Guinea species must clearly be referred to a distinct genus Proechidna.[[58]] This animal is to be distinguished by the fact that there are usually but three toes on each foot. But there are copious rudiments of the other phalanges, upon which claws are sometimes developed. The beak is curved downwards, and the back is rather arched; the whole animal has the most singular likeness to an Elephant! The ribs are increased by one pair, and there are four lumbar vertebrae. The one species is named P. bruijnii. The Hon. W. Rothschild[[59]] distinguishes a form P. nigroaculeata, which is allowed by Mr. Lydekker.
Fig. 54.—Australian Anteater. Echidna aculeata. × 1⁄6.
The Echidna feeds like anteaters, by thrusting its tongue into an ant-hill, and waiting until it is covered with indignant and marauding ants, which are then swallowed. But this animal also devours worms and insects, which are extracted from their hiding-places by the tongue. It is mainly nocturnal, and prefers the seclusion of the densest scrubs of the bush, or rocky spots where it is free from intrusion. Dr. Semon did not find that the spur of this animal was used at all in self-defence; but he thinks that possibly the weapon may be used, in the breeding season only, in the combats of the males for the females, when perhaps, as has been shown to be the case in Ornithorhynchus, the gland attached to it produces a poisonous secretion.
The egg, as it appears, is transferred to the pouch by the mouth of the mother; the shell is broken by the emerging young one, which has an egg-breaking tubercle on its snout for this purpose; the mother removes the shell. When the young has attained a certain size, the mother removes it from the pouch, but takes it in from time to time to suckle it. When on her nightly rambles the young one is left in a burrow dug for the purpose. Dr. Semon was able, from his own observations, to substantiate this act of intelligence on the part of the Echidna. It is well known that the temperature of the Monotremes is less than that of higher mammals; in addition to this fact Dr. Semon found that the range of variation of temperature in the Echidna was as much as 13 degrees or more. It is thus intermediate between the "poikilothermal" reptiles and the "homoeothermal" mammals.
Fam. 2. Ornithorhynchidae.—There is no need to attempt to define this family, since it contains but one genus Ornithorhynchus, with but one species, O. anatinus. The general aspect of the animal is well known. It is covered with dense fur of a blackish brown colour; the limbs are short and five-toed, the toes being webbed. The tail is longish and broad, being flattened from above downwards. The webbing on the anterior toes considerably outdistances the tips of the claws, as in the Seals. But this is not the case with the hind-feet. The "beak," which is broad and flat, and does actually suggest that of a duck, is not covered with horn, as is often stated, but with a fine, soft, sensitive, naked skin, which abounds in sense-organs of a tactile nature. As to characters derived from the skeleton, Ornithorhynchus has