Globigerina

“ Nor can the presence of the soft parts of the body in the shells which form the Globigerina ooze, and the fact, if it be one, that animals living at the bottom use them as food, be considered as conclusive evidence that the Globigerinoe live at the bottom. Such as die at the surface, and even many of those which are swallowed by other animals, may retain much of their protoplasmic matter when they reach the depths at which the temperature sinks to 34° or 32° Fahrenheit, where decomposition must become exceedingly slow. ”

“ The Globigerina of the present day, for example, is not different specifically from that of the chalk; and the same may be said of many other Foraminifera. I think it probable that critical and unprejudiced examination will show that more than one species of much higher animals have had a similar longevity ”

“ That Globigerina can be traced down to the Globigerinæ which live at the surface of our great oceans, and the remains of which, falling to the bottom of the sea, give rise to a chalky material. So that it must be admitted that certain species of creatures living at the present day show no sign of modification or transformation in the course of a lapse of time as great as that which carries us back to the period of chalk. There are groups of species so closely allied together that it needs the eye of a naturalist to distinguish them one from another. ”

“ Fig. 17.—Shell of Globigerina bulloides, from tow-net, showing investment of spines. (From Wyville Thomson.)
In the Perforate genera, Patellina and Discorbina, plastogamy precedes brood formation, the cytoplasms of the 2-5 pairing individuals contracting a close union; and then the nuclei proceed to break up without fusion, while the cytoplasm aggregates around the young nuclei to form amoebulae, which acquire a shell and separate. ”

“ This view has been adopted chiefly on account of the similarity of the minute organisms found to compose a considerable proportion of both deposits, more especially the pelagic Foraminifera, of which several species of Globigerina appear to be identical in the chalk and the modern Atlantic mud. Other extremely minute organisms whose nature is doubtful, called coccoliths and discoliths, are also found in both formations, while there is a considerable general resemblance between the higher forms of life. ”

“ The majority of species keep to the sea bottom; some few are pelagic, and occur in abundance on the surface of the ocean. Among the latter are the Globigerina: its shell is about one-fortieth of an inch in diameter, and usually composed of seven globular chambers arranged spirally in such a manner that all are visible from above, each chamber opening by a crescentic-shaped orifice into a depression in the middle of the next. Perfect specimens bristle with long slender spines, the pores affording passage to pseudopodia, which stream out along the spines. ”

“ They are mere live bags full of jelly, which can take almost any shape they like, and thrust out arms—or what serve for arms—through the holes in their shells, and then contract them into themselves again, as this Globigerina does. What they feed on, how they grow, how they make their exquisitely-formed shells, whether, indeed, they are, strictly speaking, animals or vegetables, Analysis has not yet found out. But when you come to read about them, you will find that they, in their own way, are just as wonderful and mysterious as a butterfly or a rose ”

“ In all seas, from the equator to the polar ice, the tow-net contains Globigerinoe. They are more abundant and of a larger size in warmer seas; several varieties, attaining a large size and presenting marked varietal characters, are found in the intertropical area of the Atlantic. In the latitude of Kerguelen they are less numerous and smaller, while further south they are still more dwarfed, and only one variety, the typical Globigerina bulloides, is represented. The living Globigerinoe from the tow-net are singularly different in appearance from the dead shells we find at the bottom. ”

“ The bed of the deep Atlantic is covered, for the most part, by a mud or ooze, largely made up of the débris of foraminifera and other minute organisms mixed with fine clay. In the North Atlantic the Norwegian naturalists call this the Biloculina mud. Farther south, the Challenger naturalists speak of it as Globigerina ooze. In point of fact it contains different species of foraminiferal shells, Globigerina and Orbulina being in some localities dominant, and in others, other species; and these changes are more apparent in the shallower portions of the ocean. ”

“ The Orbulina consists of a single cell with one orifice, but permeated by numerous microscopic pores, through which the protoplasmic material can ooze and form the pseudopodia. In the Globigerina and other genera there are several cells agglutinated together, all communicating with one another. In many species the thin cell-wall is inadequate for the wants of the structure, and an additional growth or "supplementary skeleton" is added, traversed by tubes larger, longer, and more branched, than in the first. ”

“ In fact, the living globigerina is, he says, very different in appearance from the dead shells we find at the bottom of the sea. In the living animal the shell is clear and transparent, and each of the pores which penetrate it is surrounded by a raised crest, the crest round adjacent pores coalescing with a roughly-hexagonal net-work, so that the pores appear to be at the bottom of an hexagonal pit. At each angle of this hexagon the crest gives off a delicate, flexible, calcareous spine, sometimes four or five times the diameter of the shell in length. ”

“ Protoplasmic Body and Reproduction.—The protoplasm is not differentiated into ecto- and endosarc, although it is often denser in the central part within the shell, and clearer in the pseudopodial ramifications and the layer (or stalk in the monothalamic forms) from which it is given off. In pelagic forms like Globigerina the external layer is almost if not quite identical in structure with the extracapsular protoplasm of Radiolaria (q.v.) ”

“ Every sub-kingdom of animals yields instances of the [Pg 285] same kind. The Globigerina of the Atlantic soundings is identical with the cretaceous species of the same genus; and the casts of lower Silurian Foraminifera, recently described by Ehrenberg, assure us of the very close resemblance between the oldest and the newest forms of many of the Protozoa.
Among the Cœlenterata, the tabulate corals of the Silurian epoch are wonderfully like the millepores of our own seas, as every one may convince himself who compares Heliolites with Heliopora. ”

“ At greater depths globigerina ooze is found in which the microscopic shells appear much corroded; and finally, in the deeps or areas more than three thousand fathoms below the surface, the deposit is almost free from carbonate of lime, and forms a stiff red clay composed of decomposed volcanic or atmospheric dust and those constituents of shells that are not readily dissolved by sea water. The process of formation has been clearly shown. Over the whole surface the same shell-bearing creatures die in myriads ”

“ The Mid-Atlantic swarms with pelagic Mollusca, and, in moderate depths, the shells of these are constantly mixed with the Globigerina ooze, sometimes in number sufficient to make up a considerable portion of its bulk. It is clear that these shells must fall in equal numbers upon the red clay, but scarcely a trace of one of them is ever brought up by the dredge on the red clay area. It might be possible to explain the absence of shell-secreting animals living on the bottom, on the supposition that the nature of the deposit was injurious to them ”

“ What we see in a many chambered foraminifer, such as Globigerina or Rotalia, is just the same thing, save that it is carried out in greater completeness and perfection. The little organism as a whole is not a figure of equi­lib­rium or of minimal area; but each new bud or separate chamber is such a figure, conditioned by the forces of surface tension, and superposed upon the complex aggregate of similar bubbles after these latter have become consolidated one by one into a rigid system. ”

“ Globigerina ooze may be found on the floor of the ocean at depths ranging from 500 to 2,800 fathoms of water in equatorial and temperate latitudes. The reason that it is not found in arctic seas may be that the cold surface waters of these regions do not bear such an abundant fauna of foraminifera. This is supported by the fact that it extends ten degrees farther north than south in the Atlantic, the warm water of the Gulf Stream bearing a richer fauna than the waters of a corresponding degree of latitude in the southern sea. ”

“ 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. ”

“ Each of them, however, contained carbon, and many had built lime, phosphorus, nitrogen, and other valuable substances into their bodies. Where food was abundant these grew in vast numbers, and though many are infinitely small singly, their aggregate mass is enormous. Among the tiny organisms is one called the Globigerina, a being so small as to require a microscope to study it, but in the past, as now, growing in great numbers in the sea. ”

“ Thus the microspheric Biloculina form the first few chambers in quinqueloculine succession. The microspheric forms attain to a greater size when adult than the megalospheric; and in Orbitolites the microsphere has a straight outlet, orthostyle, instead of the deflected camptostyle one, so general in porcellanous types; and the spiral succession is continued for more turns before reaching the fan-shaped and finally cyclic stage. Globigerina, whose chambers are nearly spherical, is sometimes seen to be enclosed in a spherical test, perforate, but without a pylome, and known as Orbulina ”

“ According to our resent experience, the deposit of Globigerina ooze is limited to water of a certain depth, the extreme limit of the pure characteristic formation being placed at a depth of somewhere about 2,250 fathoms. Crossing from these shallower regions occupied by the ooze into deeper surroundings, we find universally that the calcareous formation gradually passes into, and is finally replaced by, an extremely fine pure clay, which occupies, speaking generally, all depths below 2,500 fathoms, and consists almost entirely of a silicate of the red oxide of iron and alumina. ”

“ In those forms with a silicious skeleton the geometrical pattern conforms more or less to the shape of the central 491 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 ”

“ Pelagic life does not seem to be less abundant at the surface where the water is deep than where it is shallow, and it would appear that the shells must sink in such situations as elsewhere. If the lime carbonate of globigerina ooze be removed by dilute acid, the inorganic residue is similar to the red clay in the ocean-bottom. This suggests that owing to the more complete solution in the very deep water, the lime carbonate of the shells has been dissolved, leaving the red clay as a residuum. ”

“ As I have pointed out elsewhere, [7] it at once became obvious that the calcareous, sticky mud of the Atlantic was made up, in the main, of shells of Globigerina and other Foraminifera, identical with those of which the true chalk is composed, and the identity extended even to the presence of those singular bodies, the coccoliths and, the true nature of which is not yet made out. Here, then, were organisms, as old as the Cretaceous epoch, still alive, and doing their work of rock-making at the bottom of existing seas. ”

“ The animal resembled, in its extreme simplicity of structure, the minute "jelly-specks" by which the Globigerina-shells that cover the Atlantic sea-bed are even now being formed; and differed from it only as the animal of a large composite coral mass differs from that of a simple coral, in extending itself indefinitely by budding; so that a large continuous zoöphytic growth was produced, bearing a strong resemblance to a coral-reef, instead of the aggregate of minute and separate shells which formed the old Chalk, and which is even now continuing the like formation. ”

“ It has been observed, again, that the abundance of Globigerinae, in proportion to other organisms, of like kind, increases with the depth of the sea; and that deep-water Globigerinae are larger than those which live in shallower parts of the sea; and such facts negative the supposition that these organisms have been swept by currents from the shallows into the deeps of the Atlantic.
It therefore seems to be hardly doubtful that these wonderful creatures live and die at the depths in which they are found. ”