Dredged from a depth of 600 fathoms off the coast of Portugal. In life the body, or "cup," of this sponge was deep orange colour, from which the grey beard-like mass of anchoring fibres depended.
Photo by E. Connold] [St. Leonards.
CHALINA SPONGE.
A British species, composed partly of horny and partly of flinty elements.
The Animalcules, which represent the simplest and lowest forms of living animals, consist chiefly of organisms which are the equivalents of one of the single cells, or, as they might be termed, the "life-bricks," out of which all the higher animals, and also plants, are built up. They are of minute dimensions, and require the aid of the microscope for their proper investigation. Among the most highly organised members of this sub-kingdom mention must be made of the Ciliated Animalcules, or Infusoria, so called because they were first discovered inhabiting decaying vegetable and animal infusions. The so-called Slipper-animalcule is one of the commonest forms which makes its appearance amidst such environments. The length of this single-celled animal scarcely averages the one-hundredth part of an inch, but within this restricted space an amazing degree of structural and functional differentiation is included. Its outer surface is, in the first place, densely clothed with hairs, which represent its organs of locomotion. This outer cell-wall has a subjacent somewhat softer layer, in which are developed as crowded a series (as compared with the hairs) of minute rod-like bodies, which, under various stimuli, can be shot out like darts through the skin, and are adjudged to be offensive and defensive weapons, partaking much of the same nature as the thread- or stinging-cells of sea-anemones. Among other noteworthy structures, the slipper-animalcule has a distinct throat-opening, two rhythmically contracting cavities fulfilling a respiratory function and a complex reproductive nodule, or nucleus. Compared with a host of its kindred, this animalcule is a giant, the longest diameter of many of the smaller varieties measuring no more than the 1⁄5000th part of inch, or even less.
The elegant little Bell-animalcule, with its crystal wineglass-shaped body, crown of vibrating hairs, and long spirally contractile foot-stalk, is a familiar object to the possessor of a microscope. Most commonly these single-celled organisms, like the single-celled elements of organic tissues, multiply by repeated sub-division, the number that can be reproduced in a short space of time by this simple process being almost incredible. As many as a million, it has been calculated, of some species may be thus derived from an original single individual within twenty hours. In this connection these lowly organisms can among living animals most logically lay claim to immortality. The individual, in point of fact, never dies. Finding itself growing old and obese at the ripe age of, say, sixty minutes, it has simply to split itself up into two offsets, which swim away and repeat the process. Occasionally, for the rejuvenescence of the race, two individuals coalesce completely with one another, and multiplication by splitting takes place.
Some near relations of the little bell-animalcule, while sub-dividing so far as their bodies are concerned, remain united by their foot-stalks, and thus in time build up beautiful tree-like structures, laden as it were with crystal bells or fruit. In some of these the common branching foot-stalk is erect and rigid, while in others it is flexible, and contains, as in the ordinary species, a central elastic ligament. Under these circumstances the whole tree-like structure, with its crystal bells, collapses and expands again under the slightest stimulus, and constitutes one of the most beautiful objects that can be viewed through the microscope.
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.