The Naturalist in Nicaragua
is as one It is not so with the ocean—it continuous—and part was elevated and laid dry, the species could retreat to another. On the gi'eat continents the land has probably never been totally submerged at any one time; it also is continuous over great areas, and as one part
became uninhabitable, the land species could in most cases retreat to another. But for the inhabitants of lakes and rivers there was no retreat, and whenever the sea overflowed the land, vast numbers of fresh-water species must have been destroyed. A fresh-water fauna gave place to a marine one, and the former was annihilated so far as that area was concerned. When the land again rose from below the sea, the marine fauna was not retired farther back.destroyed—it simply
There is every reason to believe that the production of species is a slow process, and if fresh-water areas have not continued as a rule through long geological periods, we can see how variation has been constantly checked by the destruction, first in one part, then in another, of all the fresh-water species; and on these places being again occupied by fresh water they would be colonised by forms from other parts of the world. Thus species of restricted range were always exposed to destruction because their habitat was temporary and their retreat impossible, and only families of wide distribution could be preserved. Hence I believe it is that the types of fresh-water productions are few and world-wide, whilst the sea has mollusks innumerable, and the land great variety and wealth of species. This variety is in the ratio of the continuity of their habitats in time and space.
It follows also, from the same reasoning, that old and wide-spread types are more likely to be preserved in fresh-water areas than on land or in the sea, for the destruction of wide-ranging species is effected more by the competition of improved varieties than by physical causes; so that when variation is most checked old forms will longest survive. Therefore I think it
is that amongst fislies we find some old geological types still preserved in a few of the large rivers of the world.
To illustrate more clearly the theory I have advanced, I will take a supposititious case. In the southern states of America there is reason to suppose that since the glacial period there has been a great variation in the species of the fresh-water mollusk genus Melania, and in different rivers there are distinct groups of species. Now let us suppose that the glacial period were to return, and that the icy covering, gradually thickening in the north, should push down southward as it did once before. The great lakes of North America would be again filled with ice, and their inhabitants destroyed. As the ice advanced southward, the inhabitants of one river-system after another would be annihilated, and many groups of Melania entirely destroyed. On the retreat of the ice again the rivers and lakes would reappear, but the varieties of animals that had been developed in them would not, and their places would be taken by aquatic forms from other areas, so that the number of species would be thereby greatly reduced, and wide-spreading forms would be freed from the competition of many improved varieties.
Viewed in this light, the similarity of fresh-water productions all over the world, instead of being a difficulty in the way of the acceptance of the theory of natural selection, becomes a strong argument in favour of its truth; for we perceive that the number of marine, terrestrial, and fresh-water animals is in proportion to the more or less continuous development that was possible under the different conditions under which they lived.
The same line of argument might be used to explain the much greater variety in some classes of terrestrial animals than in others. The land has often been submerged in geological history, and the classes that were best fitted to escape the impending catastrophes would be most likely to preserve the varieties that had been developed. The atmosphere has always been continuous, and the animals that could use it as a highway had great advantages over those that could not, and so we find the slow-moving terrestrial mollusks few in number compared with the multitudinous hosts of strong-flying insects; similarly, the mammals are far outnumbered by the birds of the air, that can pass from island to island, and from country to country, unstopped by mighty rivers or wide arms of the sea.
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CHAPTER XIX.
Iguanas and lizards —Granada—Politics—Revolution— Cacao cultivation—Masaya—The Lake of Masaya—The volcano of Masaya
Origin of the lake basin.
The road passed along a sandy ridge only a little elevated above the waters of the lake, and the ground on both sides was submerged. As we travelled on we were often startled by hearing sudden plunges into the water not far from us, but our view was so obstructed by bushes that it was some time before we discovered the cause. At last we found that the noise was made by large iguana lizards, some of them three feet long, and very bulky, dropping from the branches of trees, on which they lay stretched, into the water. These iguanas are extremely ugly, but are said to be delicious eating, the Indians being very fond of them. The Carca Indians, who live in the forest seven miles from Santo Domingo, travel every year to the great lake to catch iguanas, which abound on the dry hills near it. They seize them as they lie on the branches of the trees, with a loop at the end of a long stick. They then break the middle toe of each foot, and tie the feet together, in pairs, by the broken toes, afterwards sewing up the mouth of the poor reptiles, and carrying them in this state back to their houses in the forest, where they are
kept alive until required for food. The raccoon-like " pisoti " is also fond of them, but cannot so easily catch them. He has to climb every tree, and then, unless he can surprise them asleep, they drop from the branch to the ground and scuttle off to another tree. I once saw a solitary " pisoti " hunting for iguanas amongst some bushes near the lake where they were very numerous, but during the quarter of an hour that I watched him, he never caught one. It was like the game of " puss in the corner." He would ascend a small tree on which there were several; but down they would drop when he had nearly reached them, and rush off to another tree. Master " pisoti," however, seemed to take all his disappointments with the greatest coolness, and continued the pursuit unflaggingly. Doubtless experience had tanght him that his perseverance would ultimately be rewarded: that sooner or later he would surjDrise a corpulent iguana fast asleep on some branch, and too late to drop from his resting-place. In the forest I always saw the " pisoti " hunting in large bands, from which an iguana would have small chance of escape, for some were searching along the ground whilst others ranged over the branches of the trees.
Other tree-lizards also try to escape their enemies by dropping from great heights to the ground. I was once standing near a large tree, the trunk of which rose fully fifty feet before it threw off a branch, when a green Anolis dropped past my face to the ground, followed by a long green snake that had been pursuing it amongst the foliage above, and had not hesitated to precipitate itself after its prey. The lizard alighted on its feet and hurried away, the snake fell like a coiled-up
watch-spring, and opened out directly to continue the pursuit; but, on the spur of the moment, I struck at it with a switch and prevented it. I regretted afterwards not having allowed the chase to continue and watched the issue, but I doubt not that the lizard, active as it was, would have been caught by the swift-gliding snake, as several specimens of the latter that I opened contained lizards.
Lizards are also preyed upon by many birds, and I have taken a large one from the stomach of a great white hawk with its wings and tail barred with black {Leucopternis gliiesbrcghti) that sits up on the trees in the forest quietly watching for them. Their means of defence are small, nor are they rapid enough in their movements to escape from their enemies by flight, and so they depend principally for their protection on their means of concealment. The diSerent species of Anolis can change their colour from a bright green to a dark brown, and so assimilate themselves in appearance to the foliage or bark of trees on which they lie. Another tree-lizard, not uncommon on the banks of the rivers, is not only of a beautiful green colour, but has foliaceous expansions on its limbs and body, so that even when amongst the long grass it looks like a leafy shoot that has fallen from the trees above. I do not know of any lizard that enjoys impunity from attack by the secretion of any acrid or poisonous fluid from its skin, like the little red and blue frog that I have already described, but I was told of one that was said to be extremely venomous. As, however, besides the repute of giving off from the pores of its skin poisonous secretion, it was described to be of an inconspicuous brown colour, and
to hide under logs, I should require some confirmation of the story by an experienced naturalist before believing it, for all my experience has led me to the opinion that any animal endowed with special means of protection from its enemies is always either conspicuously coloured, or in other ways attracts attention, and does not seek concealment.
About four o'clock we reached the city of Granada, and, passing along some wide streets and across a large square, found the hotel of Mons. Mestayer, where we engaged rooms for the night. The hotel, like most of the houses in the city, was built, in the Spanish style, around a large courtyard, in the centre of which was a flower-garden. Madame Mestayer was very fond of pets, and had macaws and parrots, a tame squirrel, a young white-faced monkey {Ccbus albifroyis), and several small long-haired Mexican dogs. I was interested in watching the monkey examining all the loose bai'k and curled-up leaves on a large fig-tree in search of insects. In this and other individuals of this species, a great variety of countenances could be distinguished, and I could easily have picked my own monkey out of all the others I have seen by the expression of its face. I was told that the one in the garden at Mons. Mestayer's did not touch the figs on the tree, and I believe it; the Cehus is much more of an animal than a vegetable feeder, whilst the spider-monkeys (A teles) live principal!}^ on fruits.
Granada was entirely burnt down by Walker and his filibusters in 1856, and the present city is built on the ruins of that founded by Hernandez de Cordova in 1 522. The streets are well laid out at risfht ansfles to each
other, and there are many large churches, some of them in ruins. In one of the latter a company of mounte-banks performed every evening, and the circumstance did not seem to excite surprise or comment.
The streets are built in terraces, quite level for about fifty yards, then with a steep-paved declivity leading to another level portion. One has to be careful in riding down from one level to another, as horses and mules are very liable to slip on the smooth pavement. The houses are built of " adobe " or sun-dried brick. The walls are plastered and whitewashed, and the roofs and floors tiled. They are mostly of one storey, and the rooms surrounding the courtyards have doors opening both to the inside and to the street.