[Illustration:  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, 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.

[Illustration:  FIG. 5. Sertularia tenella, HANGING FROM A SPLINT OF ROCK OVER A WATER TROUGH.  ALSO PIECE ENLARGED TO SHOW THE ANIMAL PROTRUDING.]