Inhabitants Of My Pool

The stony corallines (4, Figs. 1 and 3), which build so much carbonate of lime into their stems, are near relations of the red seaweeds. There are plenty of them in my pool. Some of them, of a deep purple color, grow upright in stiff groups about three or four [pg 371] inches high; and others, which form crusts over the stones and weeds, are a pale rose color; but both kinds, when the plant dies, leaving the stony skeleton (1, Fig. 4), are a pure white, and used to be mistaken for corals. They belong to the same order of plants as the red weeds, which all live in shady nooks in the pools, and are the highest of their race.

FIG. 4. CORALLINE AND SERTULARIA, TO SHOW LIKENESS BETWEEN THE ANIMAL SERTULARIA AND THE PLANT CORALLINE.

1, Corallina officinalis. 2, Sertularia filicula.

My pool is full of different forms of these four weeds. The green ribbons float on the surface rooted to the sides of the pool, and, as the sun shines upon it, the glittering bubbles rising from them show that they are working up food out of the air in the water, and giving off oxygen. The brown weeds lie chiefly under the shelves of rocks, for they can manage with less sunlight, and use the darker rays which pass by the green weeds; and last of all, the red weeds and corallines, small and delicate in form, line the bottom of the pool in its darkest nooks.

And now if I hand round two specimens,—one a coralline, and the other something you do not yet know,—I am sure you will say at first sight that they belong to the same family, and, in fact, if you buy at the seaside a group of seaweeds gummed on paper, you will most likely get both these among them. Yet the truth is; that while the coralline (1, Fig. 4) is a plant, [pg 372] the other specimen (2), which is called Sertularia filicula, is an animal.

This special sertularian grows up right in my pool on stones or often on seaweeds, but I have here (Fig. 5) another and much smaller one which lives literally in millions hanging its cups downwards. I find it not only under the narrow ledges of the pool sheltered by the seaweed, but forming a fringe along all the rocks on each side of the cove near to low-water mark, and for a long time I passed it by thinking it was of no interest. But I have long since given up thinking this of anything, especially in my pool, for my magic glass has taught me that there is not even a living speck which does not open out into something marvellous and beautiful. So I chipped off a small piece of rock and brought the fringe home, and found, when I hung it up in clear sea-water as I have done over this glass trough (Fig. 5) and looked at it through the lens, that each thread of the dense fringe, in itself not a quarter of an inch deep, turns out to be a tiny sertularian with at least twenty mouths. You can see this with your pocket lens even as it hangs here, and when you have examined it you can by and by take off one thread and put it carefully in the trough. I promise you a sight of the most beautiful little beings which exist in nature.

FIG. 5. Sertularia tenella, HANGING FROM A SPLINT OF ROCK OVER A WATER TROUGH. ALSO PIECE ENLARGED TO SHOW THE ANIMAL ROTRUDING.

Come and look at it. It is a horny-branched stem [pg 373] with a double row of tiny cups all along each side. Out of these cups there appear a row of tiny cups all along each side (see Fig. 5), Out of these cups there appear from time to time sixteen minute transparent tentacles as fine as spun glass, which wave about in the water. If you shake the glass a little, in an instant each crystal star vanishes into its cup, to come out again a few minutes later; so that now here, now there, the delicate animal-flowers spread out on each side of the stem, and the tree is covered with moving beings. These tentacles are feelers, which lash food into a mouth and stomach in each cup, where it is digested and passed, through a hole in the bottom, along a jelly thread which runs down the stem and joins all the mouths together. In this way the food is distributed all over the tree, which is, in fact, one animal with many feeding-cups. Some day I will show you one of these cups with the tentacles stretched out and mounted on a slide, so that you can examine a tentacle with a very strong magnifying power. You will then see that it is dotted over with cells, in which are coiled fine threads. The animal uses these threads to paralyze the creatures on which it feeds, for at the base of each thread there is a poison gland.

In the larger Sertularia the whole branched tree is connected by jelly threads, running through the stem, and all the thousands of mouths are spread out in the water. One large form called Sertularia cupressina grows sometimes three feet high and bears as many as a hundred thousand cups, with living mouths, on its branches.

The next of my minute friends I can only show to [pg 374] the class in a diagram, but you will see it under the fourth microscope by and by. I had great trouble in finding it yesterday, though I know its haunts upon the green weed, for it is so minute and transparent that even when the weed is in a trough a magnifying-glass will scarcely detect it. And I must warn you that if you want to know any of the minute creatures we are studying, you must visit one place constantly. You may in a casual way find many of them on seaweed, or in the damp ooze and mud, but it will be by chance only; to look for them with any certainty you must take trouble in making their acquaintance.

FIG. 6. Thuricolla folliculata and Chilomonas amygdalum. (Saville Kent.)

1, Thuricolla erect. 2, Retracted. 3, Dividing. 4, Chilomonas amygdalum. hc, Horny carapace, cv, Contractile vesicle. v Closing valves.

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