Fig. 13.—Living sponges.
Almost every day, for several years, I devoted one or more hours to the pastime of floating or drifting over a part of the great coral reef which constitutes the most westward portion of Florida where it reaches out in the direction of Yucatan. The islands composing the group are the Tortugas Keys, and are just above water; indeed some disappeared when a particularly heavy hurricane came, and in the center of the island upon which I lived, the water at very high tide appeared above the surface.
Among the commonest objects seen on the reef were huge vases (Fig. 13). They were found in water from a foot to fifteen feet or more in depth, and were attached so strongly to the bottom that it required considerable strength to lift them up. Some were three feet high, and I have often dived down to them and for a few seconds sat upon them as a jest for the edification of my companions in the boat above. A common name for them on the reef was "Neptune's Seats." The seats were sponges, and their collection on the Florida reef has for many years constituted an important industry, vessels being fitted out from Key West and other places for this purpose. This industry is also followed in the Mediterranean Sea, where the finest sponges known are found. To take them, men go out in small boats, and in shallow water bring them up with hooks. In the greater depths a water box is used, a box with a glass bottom, which placed over the water makes everything visible, and by this the sponger secures the sponge. Other collectors, especially those of Syria, dive for them and wrench them from the bottom, then ascend to the surface with the load. There are many different kinds of sponges, those commonly used being divided into grades, from the delicate face sponge to the coarse specimens used for washing carriages. Then there are hundreds of kinds of sponges which have no value but to form veritable mimic forest growths at the bottom of the sea (Fig. 14). Some grow upon stones or sea mud and are brilliantly colored; others again are like glass, and all represent one of the lowest forms of animal life, yet one of the most beautiful, and one that is very useful.
Fig. 14.—A sponge (Ascetta primordialis): I. o, exhalent opening; p, inhalent pores; g, ova. Starlike spicules are seen on the outside. II. Section showing pores (p), with cilia of the cells extending into them. III. Cell showing lash, or cilium. IV. Same, with lash retracted. V. Embryo of Ascetta mirabilis. VI. Section of embryo.
In handling a sponge the most indifferent person has not failed to observe two peculiarities, one that the sponge is soft, another that it is filled with holes, small and large, and has a marvelous faculty of retaining water, in which property lies its value to man. Now if we take a sponge and cut down through it, making a section, we shall find that these holes are nothing more or less than doors or mouths which lead into the interior of the sponge. If we are so fortunate as to have a live sponge to study, we shall see that water is being forced through all the small pores and out into the larger ones; and if we could examine the water, we should see that the water which passed in, is laden with living creatures which have been described in a previous chapter, while the water which is discharged contains little or no living matter. The reader will have suspected what this in-going and out-coming is. It is the operation of eating on the part of the sponge, which, while it looks very much like a plant and appears to be growing from the ground, is an animal, or a community of many cells—a many-celled animal.
Fig. 15.—Flint spicules highly magnified.
In our section of a sponge we may follow the winding channels which connect one part of the sponge with the other, and we see that the body is a mass of fibers made up of curious and beautifully shaped objects called spicules (Fig. 15). The spicules are the bones of sponges, the hard portion, the framework. In the sponge we find here and there little oval rooms, and in these are packed, side by side, minute objects with tails (Fig. 16). Each little cell has its tail upon the outside, which is really a whip or lash, used for capturing passing food. In these rooms the cells congregate and are fed by the constant onward flow of water laden with food. The food is in the shape of minute animals and plants which these little whips catch as they pass by. The whips have another purpose; their constant motion serves to force the water along through the canals, carrying air as well as food.