The Outline of Science, Volume 1

Frogs have good eyes, and the toad's eyes are "jewels." There is evidence of precise vision in the neat way in which a frog catches a fly, flicking out its tongue, which is fixed in front and loose behind. There is also experimental proof that a frog discriminates between red and blue, or between red and white, and an interesting point is that while our skin is sensitive to heat rays but not to light, the skin of the frog answers back to light rays as well. Professor Yerkes experimented with a frog which had to go through a simple labyrinth if it wished to reach a tank of water. At the first alternative between two paths, a red card was placed on the wrong side and a white one on the other. When the frog had learned to take the correct path, marked by the white card, Prof. Yerkes changed the cards. The confusion of the frog showed how thoroughly it had learned its lesson. We know very little in regard to sense of smell or taste in amphibians; but the sense of hearing is well developed, more developed than might be inferred from the indifference that frogs show to almost all sounds except the croaking of their kindred and splashes in the water. The toad looks almost sagacious when it is climbing up a bank, and some of the tree-frogs are very alert; but there is very little that we dare say about the amphibian mind. We have mentioned that frogs may learn the secret of a simple maze, and toads[Pg 217] sometimes make for a particular spawning-pond from a considerable distance. But an examination of their brains, occupying a relatively small part of the broad, flat skull, warns us not to expect much intelligence. On the other hand, when we take frogs along a line that is very vital to them, namely, the discrimination of palatable and unpalatable insects, we find, by experiment, that they are quick to learn and that they remember their lessons for many days. Frogs sometimes deposit their eggs in very unsuitable pools of water; but perhaps that is not quite so stupid as it looks. The egg-laying is a matter that has been, as it were, handed over to instinctive registration. Photo: W. S. Berridge. HARPY-EAGLE "Clean and dainty and proud as a Spanish Don." It is an arboreal and cliff-loving bird, feeding chiefly on mammals, very fierce and strong. The under parts are mostly white, with a greyish zone on the chest. The upper parts are blackish-grey. The harpy occurs from Mexico to Paraguay and Bolivia. Photo: W. S. Berridge, F.Z.S. THE DINGO OR WILD DOG OF AUSTRALIA, PERHAPS AN INDIGENOUS WILD SPECIES, PERHAPS A DOMESTICATED DOG THAT HAS GONE WILD OR FERAL It does much harm in destroying sheep. It is famous for its persistent "death-feigning," for an individual has been known to allow part of its skin to be removed, in the belief that it was dead, before betraying its vitality. WOODPECKER, HAMMERING AT A COTTON-REEL, ATTACHED TO A TREE Notice how the stiff tail-feathers braced against the stem help the bird to cling on with its toes. The original hole, in which this woodpecker inserted nuts for the purposes of cracking the shell and extracting the kernel, is seen towards the top of the tree. But the taker of the photograph tied on a hollowed-out cotton-reel as a receptacle for a nut, and it was promptly discovered and used by the bird.