No wonder, what he saw there, he could never have imagined. The stem bent; approached the button where the threads sprang, which were now all drawn in [ 80 ]the edge of the glass and attached itself there,—what was once the foot, now became the top, that too bowed and curved into a hoop; now the top let go; the animal—there was no longer any doubt that it was an animal—raised up and the threads reappeared one by one. The whole animal had moved in this unusual manner, by rolling slowly over its head.
But that strange propagation by buds, which become side branches! An animal, however simply organized, does not budge, does not grow like a tree, at least it lays eggs, from which the young animals come!
As a result, Leeuwenhoek still had his doubts; nowadays people know more about it. There his lucky star makes him think of throwing a few daphnias by the polyp into the flask. The animals are happily hopping around. The examiner squints at the polyp, holding the slide up to the light, and clearly sees the gentle movement of the undulating threads, which sometimes extend to a finger's length and become as thin as cobwebs. There a daphnia approaches one of the tactile arms of the polyp; as if struck by lightning the animal falls completely paralyzed, but it does not fall deeply, it is as if it hangs for a moment on an invisible thread,—now it sinks to the bottom and remains dead. Another daphnia touches a tentacle with its mad jumps, this animal also falls, suddenly becoming motionless, a little way down, but does not reach the bottom. The animal sticks to the feeler arm, it seems; it winds around it, and to Leeuwenhoek's indescribable astonishment, it is led by the same tentacle to the place around which all the arms of the polyp spring like a halo. There the top opens, a wide mouth opens and the daphnia is slid inside as if in a bag.[ 81 ]
Anthony van Leeuwenhoek.
Anthony van Leeuwenhoek.
[ 83 ]
The shape of the prey was clearly visible in the polyp's body. The lower part of the stipe, about a third of the whole animal, turned out to be really a stipe or a foot; so far the daphnia sags and this part was thus not hollow. The polyp, who had drawn in his arms now that he had gathered his prey, gradually thinned again, and after about four hours he was again as thin and as long as before. The daphnia was dissolved, digested, and the feeler arms groped around again, searching for a second prey.
It goes without saying that such a remarkable animal became an object of investigation by numerous naturalists. And it became more and more remarkable.
It was soon discovered that a polyp who had by some accident lost one or more of his tentacles was not deprived of it for life, but that those severed limbs grew back. They once tried how far the recovery power in the animal would go; and it turned out that it was amazing; when all but one of the feeler arms were removed, new ones appeared, sometimes more than there had originally been. This gave the polyp the name of hydra, after the monster in fables, who got a number of new ones in its place for every severed head.
Yes, in fact; if the animal is split lengthwise up to the stem, each part grows back into a new body. In the last century it was even fashionable for a while to display monster hydras at the social gatherings of nature-friends, which, mutilated in this way, bore up to thirty new branches and bodies with feeler arms on one stem.
That such experiments on animals, if taken for fun, are of no use to science is[ 84 ]clear to everyone. And although the hydra, especially because of that regenerative power, is very similar to a plant, it is still a cruel amusement; although the animal is probably not nearly as sensitive as higher animals, it is certainly not completely insensible.
There seems to be no limit to that regrowth. It seems as if Baron van Munchausen, while beating his fox, could not think of a greater lie than this: that the animal turned inside out and ran away. But this seems to be still possible with the polyp: After many failed attempts, a researcher has succeeded in turning such a freshwater polyp inside out, and lo! the little animal was very little disturbed by this remarkable operation, the outside, it seemed, served as the inside, as a stomach, and took up ordinary food.
In recent times, when in the field of the tiniest microscopic animals there seems to be not so easy news to discover as there was a while ago, the observation of larger animals and also of our native hydra has begun again. Now it has recently been shown to a Japanese naturalist that this polyp, like a captured prey a little too large for its mouth opening, turns itself a little inside out, and then spans the fringed hem of its body over the daphnia or beetle. This repulsion is so rapid that the ancient researchers of the incredible reversal experiment may have been mistaken in that, after being pulled inside out, the animal could have resumed its normal position at lightning speed.
It has now also been elucidated how it is possible that the polyp can so mysteriously paralyze a daphnia when its tentacles have scarcely touched the animal. Wonderful organs have been discovered in those tentacles with the aid of the microscope. Located in various places[ 85 ]in it cavities, in which a pointed arrow is hidden, with which a long coiled wire is fixed in those cavities of the feeler arm; something like a harpoon. At the slightest touch the polyp shoots off such a harpoon thread; if he can, several at once; the ends wind around the body of the prey and, if they hang, the polyp can grab the cable and draw its prey towards it.
But if this was not surprising enough, the remarkable animal still has a second type of hunting weapon in use. Tiny cavities in the tentacles contain a multitude of loose javelins, extremely fine needles; it uses the hydra in mass at once; a physicist examined a captive daphnia, which was about to be drawn into the polyp's mouth, and saw the creature from all sides, like a hedgehog with pins, speckled with those fine skewers. They probably serve the polyp to float a prey that is too heavy in the water, and thus keep it within its reach; this is inferred from the fact that such a hundredfold impaled daphnia floats to the surface and another dead specimen immediately sinks in the ditch water.
Such needle- or harpoon-shaped weapons of attack have also been discovered in other small aquatic animals; those threads with arrows have received the name of nettle organs, and the beasts that feed them, the name of cnidarians; perhaps to indicate the similarity with the action of the stinging hairs of the great stinging nettles.
Because of the hollow, sac-shaped body, these cnidarians are also called cavity or pouch animals. If you happen to have the opportunity to see an extensive work on zoology, you can find it described under one of these headings and become aware of many more special ones.
Only I must say that our hydra, in addition to propagation by branching, has another more animal-like one[ 86 ]way of reproduction. In the autumn eggs form at the bottom of this cavernous body; they sink to the bottom of the ditch before the animal dies and ensure that there are still hydras in the next summer.
The polyp, however, does not have a carefree life: to be destroyed without the risk of being destroyed, that would be an exception to the rule; such a thing is seldom noticed in the life of a ditch dweller.
Left: an enlarged tip of a tentacle of Hydra, t. the top b. the nettle batteries from which the harpoons are fired. Right: two greatly enlarged, nettle organs, harpoons with coiled ropes, b. the shell in which the harpoon rests, a. a point thereof which, when touched, causes the harpoon to fire, d. the stem of it. In the middle an egg of a freshwater polyp.
Left: an enlarged tip of a tentacle of Hydra, t. the top b. the nettle batteries from which the harpoons are fired. Right: two greatly enlarged, nettle organs, harpoons with coiled ropes, b. the case in which the harpoon rests, a . a point thereof which, when touched, causes the harpoon to fire, d. the stem of it. In the middle an egg of a freshwater polyp.
Like many smaller animals, it has its parasite, its predator, which attacks it and devours it alive. Sometimes a hydra is seen making unusual, violent movements; his arms brush quickly against the body and against each other, as if he were cleaning himself. And this is really the case, at least he tries, but [ 89 ]he rarely succeeds. He has been attacked by a very small mite, which literally kills him; that animal runs with its eight legs surprisingly quickly over the body of the polyp, now here, now there gnawing him. If the hydra fails to impale the mite, or at least to scrape it off, he's done with it.
Male and female of the little salamander (Molge vulgaris) Gray with brown mottled. Underside orange with black dots, the male with yellow and black spotted comb.
Male and female of the little salamander (Molge vulgaris) Gray with brown mottled. Underside orange with black dots, the male with yellow and black spotted comb.
Stroking does not always help, however, because the mite does describe a bow in the water and pounces on its sacrifice again. When the hydra is tired, the parasite begins to bite off its tentacles.
Also for some fish our hydra seems to be a delicacy, as appears in the small aquariums of the Amsterdam zoo, they catch the hydra, with the daphnia in it, away from the glass or from the water plants.
In the duck-ponds of Artis the polyps occur in great abundance; with the duckweed, which is taken out there and used in the tanks, they also end up in the aquariums. There they also cause a great deal of trouble by killing the daphnias and cyclops, which are destined for food for the fish. Not all fish attack them; the eel, for instance, with its sensitive muzzle, does not like to come into contact with the harpoons of our hydra. The water snails mow them away from the glass with their file tongues; nor should you place sticklebacks with hydras that you wish to keep alive.
The duckweed from the ponds from Artis is scooped from the ditches along the Sloter- or den Amstelveenschenweg; hydras also occur along the Haarlemmerweg, so on three sides of Amsterdam; and probably they can be found all over our country; but mostly in ditches, in which ducks and geese swim from time to time; in the dung of those birds the winter eggs of the daphnia seem to germinate well.[ 90 ]
There are different paths to take to become powerful polyps. Bring a good supply of duckweed and divide it among several bottles; let the leaves float gently on the surface for five minutes and then examine the undersides, piece by piece; they are also common on the underside of the water lily leaves; the brown spheres look a lot like water snail or beetle eggs, but when thrown into water they very quickly take on the unmistakable polypen shape.
Another less time-consuming remedy is this: Toss a mass of duckweed into a bucket of water, stir it vigorously for a while with a stick, then quickly pour the water, without the duckweed, into a white bowl and the polyps that fall to the bottom, where you can suck them in with the help of a thin tube. You know, by making use of the air pressure on the water: keep your thumb on one open end of the tube, put the other end in the water above the polyp, thumb off (the water rises with the polyp in the tube) put your finger back on it, and transfer the contents where you want them.
But, ne cherchez pas midi à quatorze heures! what you are trying so hard to get is very often so close to being taken.
It has happened to me more than once that I have searched long and in vain for hydras, only to find by chance that I had them at home for a long time.
Male of the Alpine salamander, in splendid plumage. The comb is white with black; the side stripe light blue; the belly and chest are solid orange-red.
Male of the Alpine salamander, in splendid plumage. The comb is white with black ; the side stripe light blue; the belly and chest are solid orange-red.
In that shady jungle of duckweed, the roots of which form the trunks and the rounded leaves form the dense foliage, lives a world of all kinds of creatures, which are not so easily noticed. If you now create a net full of that duckweed, just to bring shade and food into the aquarium, then so much will come in that it will not take until later[ 93 ]is noticed; and if you transplant larger aquatic plants straight from the ditch into it, the chances are even greater that one day you will gladly discover that you already have freshwater polyps.
And very often larvae of salamanders immediately enter. They usually keep their gills until late summer; this makes them easy to recognize and distinguish from tadpoles; because these already lose their gills in the first weeks of their existence, most tadpoles have already been promoted to young frogs during the summer vacation.
Such salamander larvae should be reared. That is not difficult at all, because the creatures eagerly eat all the small good of the ditch water and also like very small earthworms; they grow quickly. If you feed them well in the autumn and keep them in a room that is not too cold in the winter, they will continue to eat and grow; and then you have the chance to see an adult salamander in its splendid plumage in the spring at the last moult of winter; the animal is small in stature in the first year, but the colors are already quite beautiful. One hundred to one, that the larvae you get when you scoop up daphnia is one of the common little newt: Triton taeniatus or Molge vulgaris, the last name being the correct one. But it is possible that there is a larva of the great newt (Molge cristata or crested newt); this is a fairly rare animal for our country. But the rarest of all is the Alpine salamander (Molge alpestris). This was first discovered in our country a quarter of a century ago (1895), by H. Beker, the son of a pharmacist in Breda, later (1896) Chr. H. J. Guess a large number of them caught near Groesbeek. Anyone who catches such salamanders, or knows where they have been caught by others, should write a note to[ 94 ]"The Living Nature" in which the first finds are also mentioned. Just write me or Thijsse's name; but only with “De Levende Natuur” Amsterdam, as the address, does the postcard also end up.
These salamanders are actually not real aquatic animals, they can only be found in the ditch in the spring, after laying eggs they go ashore. In fact, they do not belong in ditches and puddles; but the chance of creating larvae is quite high, so I have only briefly outlined the three species for you; so that you can easily distinguish them from one another, should chance ever throw larvae of different kinds into your hands.
Such animals with a double life are more to be found in the ditches and puddles; for a while they carry aquatic life, and one day take up aerial life. And it is sometimes difficult to make people, who have not yet learned and read so much, believe that the larvae of such an hermaphroditic animal and the adult animal are one and the same being.
Especially among the duckweed many of these animals live in a larval state, where they seem to feel safer than in the lower layers of the water.
Also with the transferred snail shells something else comes in. If you now and then sit and gaze for fifteen minutes at the small piece of nature with which you have decorated your house, you may notice an inexplicable movement in small hollow reed pieces, in clinging leaves, in small empty or inhabited snail shells, which seem to stick together, in the shells of the freshwater mussels—which have already entered the aquarium, without you knowing how—yes, movement in clumps of sand sometimes.
An old male of the Greater Newt or Great crested newt (Molge cristata) in the splendid plumage; the underside is orange with black mottled.
An old male of the Greater Newt or Great crested newt (Molge cristata) in the splendid plumage; the underside is orange with black mottled.
That enigmatic movement, that sliding on or that[ 97 ]the floating of inanimate objects in still water ceases as soon as you touch those objects with a stick. If you come and have a look again about eight days later, those strange things have become bigger; the fine leaves, the mussel shells and snail shells have grown together into elongated tubes, into tubes, into boxes, into nests, sometimes round, sometimes square, sometimes hexagonal.
Tube larvae of live snail shells, mussels, duckweed leaves and other material.
Tube larvae of live snail shells, mussels, duckweed leaves and other material.
Of course you need to know more about that, and you will soon succeed. Look, there's something black coming out of the front and widest opening of that 2cm. long hollow pipe out; a head, a chest, 6 legs, that's all! It's gone again!
A larva, you say at once; yes, a larva, but of a special kind, a hermit, who never leaves his cell more than halfway, at least not voluntarily.[ 98 ]
And he needs that shelter, his abdomen is so soft, the chitin skin there is so thin that a single bite of a beetle or a thorn would cost him his skin.
That is why, like the hermit crab—of which you have certainly heard, and which also has such a difficult, weak abdomen—it puts its weak side in a shell that is not so easy to bite through. The lobster usually does this in a stolen or found house of a sea snail, a so-called whelk or whooping perch—our tube larva is less thieving in nature: it builds its house itself.
The lime, or rather the glue, he has with him, and with beak or paws he bites, and kneads and glues until his vault is to his taste. He holds himself in the back with a pair of hooks, and about his abdomen he has a net of silvery threads, between which the necessary air is kept; air-tubes terminate in between, which draw on the supply when necessary.
Now I'm sure you'll be able to get such a phryganide (that's the learned name for these interesting little creatures) out of his locker one day. That can do no harm, even if the animal is not fond of it at all. Take it separately on a saucer. Gently push a pinhead against his abdomen; if he doesn't want something more intrusive. There he is out! What a clumsy creature! Seesaw, he's already back in it, with his head forward he has crawled into his shell. Check it out! Weird, is not it? He's in good shape again, the head for the opening.
If you take his house away, when he has been driven out, he will look for all kinds of sunken leaves, sticks, shells, fine stones, to make a new home in haste. [ 99 ]to make. However, it is not nearly as beautiful and sturdy as the previous one.
If they have sufficient stock of building material, each species chooses its own material and always adheres to a fixed building order. And there are many species, so that a collection of phryganid houses can offer a rich variety.
The picture here shows some of the most beautiful shapes. Here and there you see the head and legs of the tube larva sticking out of the house. Some apparently only used snails or mussel shells, others only used vegetable building materials, I found one that was made entirely from empty beech nuts.
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