Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.
NOCTILUCAS.
These are the animalcules which chiefly produce marine phosphorescence.
There are other animalcules nearly allied to Noctilucas which sometimes occur in such vast abundance in both salt and fresh water as to visibly affect its character. In addition to a very long lash they have a girdle of vibratile hairs. The fresh-water representatives of this group are sometimes brilliant green, at others bright scarlet. That instance among the Biblical Egyptian plagues in which the water of the Nile was as it were "turned to blood, and all the fish died," has been attributed to a phenomenal development of these animalcules, which, on dying, polluted and putrefied the water. Instances of fishes being destroyed in vast quantities through a like agency throughout even extensive sea-areas have been occasionally recorded. While these pages are going to press an account has appeared in an American journal of red water caused by these flagellate animalcules, which occurred last July for an extent of at least 200 miles along the coast of California, producing with their decomposition a most sickening odour, and the death of shoals of fishes, octopods, sea-cucumbers, and other organisms.
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.
POLYCYSTS.
Flinty-shelled organisms of microscopic dimensions. The living animals consist of tiny specks of transparent jelly, from which radiate innumerable false feet of hair-like fineness.
Next to the Flagellates come the Root-footed Animalcules, which possess no mouth and no hairs or lashes, but progress by pushing out lobes of their jelly-like substance in any desired direction, into which the rest of the body flows. Food is picked up at any point with which an acceptable morsel may be brought in contact. The little gelatinous animal known as an Amœba is one of these. Related forms of this jelly animalcule secrete shells of varying form and structure. Some of these, known as Forams, are of carbonate of lime, and wonderfully like nautiluses and other of the higher molluscan shells in aspect. Though so minute, scarcely visible to the unassisted eye, they occur in the sea in such numbers as to form by their aggregations the more considerable ingredients of vast areas of the earth's strata, both past and present. The chalk cliffs of Albion and the white tenacious ooze of the broad Atlantic are thus to a large extent composed of the shells of minute organisms, which formerly flourished near the surface of the ocean, but sank on their death to its abysmal depths.
The simplest of the forams fabricate shells with a single chamber, which are often elegantly vase- or flask-shaped. More usually, however, the shell represents the product of repeated buddings or outgrowths, and may attain considerable dimensions. Flattened circular forms of this type much resemble time-worn coins, and are hence called Nummulites. Their fossil-shells enter mainly into the composition of rocks which extend through North Africa and Asia to the Himalaya, and supplied the stone of which the Pyramids are built.