out; they then coat themselves with a crust of earth, and are dependent on their lungs for every breath they draw. During the rest of the year they can use either these or their gills.
The close relation between fish and amphibia is established in yet another way by the Caudata, which retains its gills and does not lose them, as do its relatives, the frog and salamander. The olm of the Adelsberg grottoes also belongs to this class; it is an animal of a pale-red color, which spends its existence in subterranean darkness. Its eyes, as is also the case with other animals that live in constant darkness, are not developed, there being no possible use to which they could be put; they are very small, and lie beneath the skin.
A connecting link between the birds and the reptiles is found in the fossil archæopteryx brought to light in the slate-quarries at Solnhofen; the feathers denote a bird, the rest of the body is that of a reptile. The Ornithorhynchus paradoxus of Australia serves to connect the feathered tribe with the mammalia. It lives in seclusion in dreary regions on river-banks, and builds its subterranean home in such a manner that one of the two exits is always submerged by the stream. It has four feet, and a broad bill, with horn plates on the edges like that of the duck, and seeks its food like this fowl. At the foot of the male there is a spur corresponding to that of a rooster; between the toes are webs like those of water-fowl. It would hardly seem surprising to find this strange creature, in many respects so like the birds, propagating its kind by eggs; but it is a true mammal, and gives birth to live young.
The transition from the palms of the tropics to the palms of the north—the fir-trees—is made by the shining cycadees, whose leaves, as emblems of peace, are placed on tombs. The guetacea must also be regarded as intermediate between the lower and the higher orders of plants. To these belongs the curious "welwitschia" of Africa, the thickness of whose stem exceeds by three times the height. During its whole life—over a century in duration—it bears only two, but very large, leaves, fully two metres in length and one metre broad; it is well named "the wonderful."
At first sight the assertion may seem strange, that the dividing line between the animal and the vegetable kingdom is not definite, and that one may sometimes be in a quandary to know whether he is dealing with an animal or a plant. That the rose must be accounted a plant there can be no doubt; and that the gaudy butterfly, coyly hovering above it, must be classed with the animal kingdom, remains unquestioned. But it is by no means so easy a matter to determine the nature of that peculiar being which we find in damp moss. It is a slimy mass, but little colored; it moves slowly and in every direction, yet no feet are discernible. After a long dispute the botanists have had to accept into their realm these slime-fungi, for during a part of their existence they are distinctively plants, and propagate by spores.
