Photo by Saville-Kent, F.Z.S.] [Milford-on-Sea.
A GIANT SEA-ANEMONE.
Measures, when opened, 18 inches in diameter. Is almost always associated with companion or "commensal" fish and crabs of brilliant colour. The fish cruise round in search of food, but always return to shelter among the anemone's tentacles. Photograph taken through the water.
Many jelly-fishes possess an unenviable reputation with reference to their stinging properties. The so-called Portuguese Man-of-war is one of the more noteworthy of these. The organism consists of an ovately pointed air-bladder, which floats on the water, and from which depend numerous nutritive polyps and a mass of capturing-filaments, or tentacles.
CHAPTER VII.
SPONGES AND ANIMALCULES.
The Sponges are regarded as a group standing on the borderland between the Polyps and the lowly organisms which follow. The familiar Bath- and Toilet-sponges of commerce represent but an insignificant fraction in comparison with the many hundred species which find no place in the world's market. Toilet-sponges owe their intrinsic value to the relative fineness and elasticity of their component fibrous skeletons. In these particular species the skeleton is composed of a substance akin to horn. In other sponges the skeleton may consist of horny fibres mixed with flinty spicules, or it may be of flint only, or of spicules of carbonate of lime. Finally, there are sponges which possess no internally supporting skeleton, fibrous or spicular, and whose substance is consequently little more than gelatinous. All these numerous forms, however, agree with one another in the identity of their most essential vital elements. In the living sponge the skeleton, fibrous or otherwise, is embedded within a gelatinous matrix by whose component cells it is excreted. Externally the sponge-body is perforated over the greater portion of its extent by minute holes or pores, while one or more holes of relatively large size occupy the summit of the sponge, or are scattered here and there among the numerous smaller pores. The smaller pores represent incurrent apertures, and lead to chambers within the sponge's substance lined by cells. Each of these is provided with a long whip-like appendage, with a transparent wineglass-shaped cup or collar, which is a beautifully constructed food-trap. The lashings of the whips of the collar-cells cause currents of water bearing nutrient particles to flow in at all the smaller pores. Arriving at the chambers, these particles are caught by the outstretched collar-traps and absorbed into the cell's substance. The water, together with rejected and waste materials given off by the sponge-body, is carried forward, and passes out at the larger orifices or vents.
Photo by W Saville-Kent, F.Z.S., Milford-on-Sea.