BY SARAH COOPER.
SPONGES GROWING.
Sponges are so common and so familiar that many of us have used them all our lives without stopping to admire their curious and interesting structure, or to inquire into the history of their past lives. We may, indeed, have noticed that they can be squeezed into a very small space, and that they will return to their natural shape when the pressure is removed. We have perhaps noticed also that they are full of little holes or pores, and that they will absorb an astonishing quantity of water.
You know there has been a doubt whether sponges belong to the animal or to the vegetable kingdom. For a long time naturalists were in doubt about the matter, but it is now settled that they are animals, living and growing on the bottom of the ocean. The only part of the sponge that reaches us is the skeleton. The living sponge is a very different object. Shall we see what we can find out about it?
Upon naming the word "animal," a picture comes before our minds of some creature having a mouth to eat with, and eyes to see with, and possessing feet or wings, or some other means of moving about; but the sponges are far from this. They are probably the lowest animals with which you are acquainted. They have no nerves, no heart, no lungs, no mouth, and no stomach.
Fig. 1.—Group of Spicules.
Live sponges consist of jelly-like bodies united in a mass, and supported by a frame-work of horny fibres, and needle-shaped objects called "spicules,", which you will see in Fig. 1, and which we must examine further after a while. This jelly-like flesh, covering all parts of the skeleton, is about as thick as the white of an egg, but it decays immediately after the death of the sponge. During life the flesh presents many bright colors; in some species it is of a brilliant green, while in others it is orange, red, yellow, etc.
The frame-work varies in different kinds of sponge. In those which are valuable for our use it consists of horny fibres interwoven in all directions until they form a mass of lacy net-work. This you can easily see with the naked eye, but by looking through a microscope you will see beauty you had not imagined, and which but for this valuable instrument would never have been dreamed of. In our ordinary sponges these fibres are all that remain of the former living-animal, the soft flesh having been removed. It is found that the horny fibres are composed of a substance very similar to the silk of a silk-worm's cocoon. They are exceedingly tough and durable. Most of us have discovered that a good sponge becomes like an old and tried friend, and that unless it is abused it seems as if it might never wear out.