'Water, Water, Everywhere'
FOR days the great forests around my camp in the high Dominican mountains had been swept by those torrential rains and winds known only in such places. At first they inspire one with awe, but later one becomes accustomed to their uninterrupted violence and settles into a state of stoic resignation. Few places in the world experience a greater rainfall than these cloud-swept mountains. Everywhere one hears the boom and roar of tumbling waters. Cloud-bursts not infrequently move trees and earth and boulders to the valleys. At times it is erosion before one’s very eyes. Perhaps during the wet months of January and February one may experience short stretches of sunlight, but while I worked in the mountains at this time its tonic rays were few and far between.
At night, in this jungle and precipitous world, exotic sounds add excitement to life. They bring that sensation of total ignorance of their sources that the explorer so often experiences while working a new country for the first time.
There was a creature called by the natives the blacksmith beetle. After nights on end of searching and trying to outwit his uncanny ventriloquial powers, he proved to be a huge and musical tree cricket that filled the forests with ringing sounds which might have been vibrations from a thousand tiny anvils. Harsh, almost deafening noises issued from the bodies of huge locusts in spiny armor. They called from the high forests, or from the sides of the camp buildings, ‘ Crackcrack, crack-crack, crack-crack!’ If one should have the fever, their monotonous calling would seem to say, ‘All night, all night, all night,’ and sleep would be quite banished by them.
In the walls there were ghostly tappings, now here, now there, now overhead. When I found the animal that produced these sounds I could hardly believe my eyes, for no living creature is a more frightful-looking monster in miniature than these tapping, ghostlycolored gecko lizards. They liked the dark hiding places in the loose boards of the roof. Better still they liked the moths and roaches, and their tappings signaled satisfaction at conditions in general.
Again there were the colonies of strange bats who lived behind the shingles. Some fed their babies periodically during the night, some stayed away till morn; all caused a peeved or jocund din, according to their everchanging moods.
From the dense gloom all about me came the more musical sounds from the blown-up throats of tiny tree frogs. The wetter the night, the more they sang, and by the light from my hurricane lanterns I could watch their impassioned choruses from low and dainty leafen platforms.
They were beautiful, big-eyed creatures in various shades of brown, with that amazingly wide-awake appearance that only a wet and delighted tree frog can assume. From those tiny throats bubbles of cream-colored skin were inflated into big balloons, and as these pouches rose and fell there came the sweet and penetrating notes, ‘Co-leet, co-leet,’ from dusk till dawn, and the ladies of their kind must have been charmed indeed by such dulcet ardor.
Being especially upon the lookout for such amphibian creatures, I was of course delighted by their numbers. Here was a much-sought-after frog suddenly become common. On every side their voices rose from the darkness. Would it not be the easiest thing in the world to find their eggs, and their tadpoles, and to record their habits of life? Yes, it would be very simple to add to the history of this creature something besides the burdensome title of Eleutherodactylus martinicensis.
Dominica is a country of tremendous rainfall. The hot tropical sun above the island sucks up enormous quantities of water from the surrounding seas, and the high cold-topped mountains draw it back again from the dense clouds that are ever forming about them. There are rivers, streams, and brooks of every size, — one, in fact, for every day in the year, according to one of my men, — and therefore it should be the ideal home for amphibian life.
My search for the jelly-like eggs began at once. The first day yielded nothing at all, save a tired pair of legs and fuel for my enthusiasm. The second day went by like the first, with my collecting tins empty, and so did the third and fourth. A week went by, two weeks, a month, two months; and, with all this rain and all these frogs, not an egg could I find.
I thought at first that I had not struck the breeding season, but during the first part of the third month of my search I decided to sit down in solitude and ponder the whole question. In a short time I had found one important answer to the mystery. With all this water and rainfall, there was really no suitable water for my frogs!
The rivers were at once too large and too swift for the singly deposited eggs of frogs. They would be washed away at once to the sea. The smaller streams were rain carriers from the high mountains. They might be filled and churning with foam to-day, but empty tomorrow, or as soon as the rains let up for a day or two toward the approach of the dry season. Of still pools there were almost none, for most everything is a side hill in Dominica. What pools I did find were inhabited by the fierce, predacious young of dragon flies, whose favorite food would soon become the succulent tadpoles, were there any to be had. The water-holding leaves of those numerous tropical plants called bromeliads would have made excellent depositories but for the ever-hunting and ravenous bands of brown birds called trembleurs.
In Dominica the frogs are confronted with the anomaly of a world of water, but none for their all-important purpose of depositing their eggs. What, then, could be the answer to such an interesting puzzle?
Time went on. The end of my expedition was in sight and still the mystery remained unsolved. Then suddenly I found the answer. On the damp forest floor, beneath huge trees and tangled vines, I saw the crystal-clear eggs of my frog. With them came a story of intense and absorbing interest, a story whose kind is the lure that sends naturalists to the ends of the earth, for a single revelation such as this repays the traveler for his labor and expense a thousandfold.
The eggs lay sparkling on the black mould, not in a mass, but strung out in small groups, or singly, over ten inches of ground. No jewels were ever discovered with greater satisfaction, or removed to any camp with tenderer care. In a few days’ time I saw with delight that the cream-colored embryos were actually developing into minute frogs!
Each still possessed a tail, vestige of appendages of once free-swimming tadpoles. How long ago must it have been that this species passed through the usual stages of egg and tadpole to frog? Why has it evolved in such a manner as to do away entirely with the waterliving larva? The questions answer themselves when we review the conditions which the frogs must meet.
Before I knew the whole truth of the story the comparatively huge size of the eggs appeared at once significant. It seemed certain that there must be something very unusual about a mature frog measuring one inch in length that laid eggs upon the bare ground, each of which was nearly a quarter of an inch in diameter.
At home our big garden toads and pond frogs do nothing like this. They place their eggs in water and each individual sphere is quite small, perhaps only an eighth of an inch in diameter. How, then, did the ponderous eggs of our little Dominican frog evolve?
Let us suppose that, however and whenever the species reached the island, it first deposited its eggs in such water as it could find that seemed suitable for the purpose. Such could only be had in the form of rapidly drying rain pools, or water caught in leaves. As the species lives mostly upon the ground, although a ‘tree’ frog, the bromeliads eliminate themselves, even disregarding the hunting birds, and we are reduced to the ground form of water supply.
In a normal frog’s egg the embryo moves to the outside of the jelly covering as the development proceeds, where it remains for a time before taking up its swimming life; but, if it were to find itself in a dry medium upon arriving outside the egg, would not the normal reaction cause it to wiggle back into the more hospitable jelly ? This would not require intelligence — it would simply be automatic under such conditions; and thus, I believe, the first of our frogs in question may have acted when they found themselves in a dry ‘ pool.’
In the beginning many must have died; but natural selection entered here, and those eggs that contained the greatest amount of food matter — for there is variation in everything of this sort — produced the tadpoles that survived the longest, and some of these eventually reached maturity.
Thus may the seed have been sown that has borne a frog without a tadpole. Generation after generation may have left the eggs, at periods, ever so slightly later in their lives. Under these conditions, as I have stated, the largest eggs continued to produce the surviving individuals, and thus the greater food mass and the more advanced frog were evolved together.
To-day we see the tadpole stage of old within the egg. The tail is there, but, being now useless, it soon disappears and the creature steps out into the world a tiny but perfect frog, direct from the egg! Behold, then, a frog that has risen, at least in its life history, to a plane beside the reptiles — the next higher class of living creatures!
To watch the rapidity of this mite’s development within the glasslike egg is a joy and revelation. At first there is nothing but a cream-colored yolk within a sphere of crystal. Soon the embryo appears, lying as though nursing upon its soft bed of rich nourishment. It is cream-colored also for a time. It grows and lengthens as the days go by, and the power of motion comes to its feeble, budding limbs and tail.
In the middle of its egg-life, it becomes very active, lashing its tail energetically at the slightest disturbance from the outside. When I picked up the first partly developed eggs, each embryo protested thus with a remarkable exhibition of energy.
More days pass and pigment commences to cloud the creature’s creamy tissue. It comes in tiny stellate forms of black that throw lengthening arms through the flesh like the streamers from a bursting shell. These meet others in their living flight, and so at last color flows through every cell of the tiny body. Finally there comes the day of emergence. Out steps the tiniest frog, all moist with birth; and, peering from wide and glorious orbs of black and gold, he mounts another egg, or perhaps a leaf upon the forest floor, and surveys the great jungle that is to be his home. A mere speck in a world of strife.
It is all so delicate, so beautiful and mysterious, one marvels at the teachings of this great free school. My frog is only one of Dominica’s mysteries. It is a child of a land peculiarly endowed with anomalies.