The phosphorescent power is by no means confined to the fishes proper of the deep sea. Starfish and most of the various forms of zoophytes possess it, though in less perfect organs. One poured out “clouds of a pale-blue, highly luminous substance, which not only illuminated the observer’s hands and surrounding objects in the vessel in which it was confined, but finally communicated a luminosity to the water itself;” another threw out light of a brilliant green, coruscating from the centre, now along one arm, now along another. In view of the phosphorescence even of the surface of the sea when full of luminous creatures, it is not rash to conclude that the eternal night of the abyss is in places lighted with sufficient brilliance by its phosphorescent zoophytes and fishes. Where these are few or absent, there must be darkness either partial or complete. Hence we are presented with the perfectly reconcilable contradiction of deep-sea creatures with eyes of high development, and others with no eyes at all; one species possessing eyes with four thousand facets, while crabs and prawns are found totally blind, like the fish of subterranean caverns. Those which carry lamps themselves, or live among luminous creatures, not only retain their eyes, but are supplied with organs of abnormal power in order to use to the utmost the phosphorous beams. The presence of bright colouring in the deep-sea forms is also explained in the same way, so far as colour is related to the presence of light. There is little difference in the hues of deep-sea and shallow-water species, except that shades of red are more frequent in the former, possibly because red is the complementary colour of the phosphorescent beams.
It is in the leading facts which make such minor developments possible that the wonder and significance of these discoveries lie,—in the defiance of such physical obstacles as are set to life by enormous pressure, and in the artificial lighting of the abysmal darkness by the invading creatures. Sir Richard Owen once suggested an extension of the limits of terrestrial life, by pointing out that the light of the planet Jupiter was suited to the form of the vertebrate eye. When the mind which has once grasped the physical conditions of the ocean abyss, is confronted with the triumph of living creatures over such surroundings, it no longer lies with it to reject as impossible the surmise that life, which so transcends the limits set by ordinary experience to its scope on earth, may also extend to the planets.
THE LION HOUSE AT THE ZOO.
[“Hic habitat leones.”—Old Map of Central Africa.]
Just fifty years ago, when the best means of keeping wild animals in health and vigour when confined was still matter for experiment, an interesting set of statistics of the length of life of the large felidæ in the Gardens was submitted to the Society by Mr. Rees. It appeared from the records of the menagerie that lions, leopards, tigers, and pumas only lived, on an average, for two years in the Gardens, which gave a rate of mortality of about one per month. The value of lions and tigers was then about £150 each, and of leopards and pumas £15.
The system which led to this great mortality was one of confinement in small stuffy cages, in a room artificially heated throughout the year, and much was hoped from a complete change of treatment which had just begun.
Pumas. From a photograph by Gambier Bolton.
The new principle was one of “free exposure to the outer air, with no artificial heat whatever,” and the range of dens now known as the “Terrace,” on either side of which the bears are kept, was built for the accommodation of the lions and tigers. The cages do not strike us as particularly roomy or comfortable now, but at that time they were looked upon as unusually spacious, and the unfortunate carnivora, which had been boxed up in stuffy rooms and narrow cages, soon felt the benefit of the change. The African leopards, which were emaciated and sickly before their removal, became plump and sleek in a fortnight, and the appetite of all materially increased. The most convincing proof of this gratifying change was that a tigress, feeling hungry in the night, killed a tiger, and a puma did the same, and partly devoured its mate. The Society took the hint, and increased their rations, and for some time the new method of lion-culture answered well.