Fig. 329.—Globigerina and other bodies taken in deep sea soundings (Atlantic).
“Many of the forms,” writes Major Owen,[64] “have hitherto been claimed by the geologist, but I have found them enjoying life in this their true home, the silicious shells filled with coloured sarcode, and sometimes this sarcode in a state of distension somewhat similar to that found projecting from the Foraminifera, but not in such slender threads. There are no objects in nature more brilliant in their colouring or more exquisitely delicate in their forms and structure. Some are of but one colour, crimson, yellow, or blue; sometimes two colours are found on the same individual, but always separate, and rarely if ever mixed to form green or purple. In a globular species, whose shell is made up of the most delicate fretwork, the brilliant colours of the sarcode shine through the little perforations very prettily. In specimens of the triangular and square forms ([Plate III]., Nos. 43, 44, 45 and 46), the respective tints of yellow and crimson are vivid and delicately shaded; in one the pink lines are concentric; while another is of a stellate form, the points and uncoloured parts being bright clear crystal, while a beautiful crimson ring surrounds the central portion. A globular form resembles a specimen of the Chinese ball-cutting—one sphere within another; this, however, appears to belong to a distinct species.
Fig. 330.—Globigerina and other bodies taken in deep sea soundings, 1856 (Atlantic).
“The shells of some of the globular forms of these Polycystina, whose conjugation I believe I have witnessed, are composed of a fine fretwork, with one or more large circular holes; and I suspect the junction to take place by the union of two such apertures. That the figures of these shells become elongated, lose their globular form after death, and present a disturbed surface is seen in some of the figures represented in [Plate III]., Nos. 82-85.” Those without internal chambers have been described as Orbulina universa, [Plate III]., [Fig. 78], while Nos. 75 and 76, although members of the same family, have been separated, but all should certainly be united under Globigerina.
“The minute silicious shells of Polycystina present wonderful beauty and variety of form; all are more or less perforated, and often prolonged into spines or other projections, through which the sarcode body extends itself into pseudopodial prolongations resembling those of Actinophrys. When seen disporting themselves in all their living splendour, their brilliancy of colouring renders them objects of unusual attraction. It will appear that they wish to avoid the light, as they are rarely found on the surface of the sea in the daytime; it is after sunset and during the twilight that they make their appearance.”
Many forms of Globigerina and Foraminifera are represented in Figs. 329 and 330. These varied and beautiful forms were dredged up with soundings made in 1856 for the purpose of ascertaining the depth of the Atlantic, prior to the laying down of the electric telegraph wire from England to America, and taken at a depth of 2,070 fathoms.
Heliozoa.—Actinophrys-Sol, “sun-animalcules,” belong to this group; most of them inhabit fresh water ([Plate III]., No. 66). The chief characteristic, and the one to which they owe their name, is the possession of long, slender, somewhat stiff pseudopodia; these radiate from all parts of the body. The living animal usually contains green-coloured particles within a minute translucent spherical globule of about 1⁄250th of an inch in diameter. It is, therefore, variously designated the green sun-animalcule, Acanthocystis, or Actinophrys-Sol. It is commonly found amongst the weeds in clear pools of water, where desmids abound. The pseudopodia appear to be stiff; they are, however, quite flexible, and the body contains more than one clear vesicle with a nucleus; reproduction is secured by the simple division commencing in the nucleus. The little animal can move over a hard surface by the alternate relaxation and stiffening of its pseudopodia; when one of these touches a small organism, it is believed to paralyse it, then envelop, and deliberately digest it. In another species, the lattice-animalcule (Cathrulina), the pseudopodia or silicious threads are arranged tangentially. It grows on a long flexible stalk, attached to an aquatic plant, the total length of which is about 1⁄200th an inch. The globular body is perforated in all directions, through which the fine stiff pseudopodia are thrust out; it is often known to form colonies.
In this order may well be placed the Radiolaria; they are, however, usually separated. But Radiolarians, whether seen alive or in their skeleton form, are surpassingly beautiful. By the favour of Messrs. Warne, I am enabled to append a frontispiece plate to this volume taken from their “Royal Natural History.” These bodies are all marine, and live in zones of several thousand fathoms, and like their congeners, the Globigerina, they avoid a strong light, and only appear after sunset. Their bodies are supposed to emit a phosphorescent glow, but more is known of their silicious skeletons than of their living forms; yet it is not this feature that separates them from other orders of rhizopods, but the possession of a membranous central capsule enclosing the nucleus. The body substance outside this capsule is highly vacuolated in some species, especially in surface forms. A few are without a skeleton, and these consist of oval masses of protoplasm, with slender pseudopodia. In a few species the skeleton is formed of a glassy horny substance, termed acanthin, arranged in the form of radiating spines.
Radiolarians secrete a silicious skeleton, which assumes a variety of forms, as trellis-work, boxes joined by radiating spines, helmets, baskets, bee-hives, discs, rings, and numerous other forms. Haeckel has described upwards of four thousand species, and possibly as many more could be added to this number. Radiolaria are divided into two groups. In the one there is either no skeleton or one of silex; in the other the skeleton is formed of radiating spines of a horny nature. These are again subdivided according to the characters of the central capsule. In those forms with a silicious skeleton the geometrical pattern conforms more or less to the shape of the central capsule, being either spherical or conical. The central capsule is regarded as being homologous with the calcareous shell of Globigerina. Reproduction takes place by simple division into two, or by the body breaking up into spores, each provided with a flagellum, or two spores may fuse together, and the result will be an adult Radiolarian. Certain yellow corpuscles present in the outer part of their body-surface change into unicellular parasitic algals; these can be separated and cultivated independently of their host. The Radiolarians live floating at all depths from 1,000 to 2,500 fathoms, and are distributed over areas in the central Pacific and the south-eastern part of the Indian Ocean, the ooze forming the ocean bed being made up of their skeletons to an extent of 80 per cent. of the deposit; hence it has become known as Radiolarian ooze. The chalky-looking Barbadoes earth, a Tertiary formation, is composed almost entirely of their skeletons. Somewhat similar deposits exist in the Nicobar Islands, in Greece, and in Sicily.