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Take away the cysts which characterize the Radiolaria, and a dead Sphærozoum would very nearly represent one of this deep-sea "Urschleim," which must, I think, be regarded as a new form of those simple animated beings which have recently been so well described by Haeckel in his Monographie der Moneras. So it received the name of Bathybius Haeckelii.
Nevertheless, the positive and negative evidence all points the other way. The skeletons of the full-grown, deep-sea Globigerinæ are so remarkably solid and heavy in proportion to their surface as to seem little fitted for floating; and, as a matter of fact, they are not to be found along with the Diatoms and Radiolaria, in the uppermost stratum of the open ocean.
As we saw, one of the early requirements to be fostered by natural selection in the Archaean struggle for life was a "thick skin," and the thick skin had to be porous to let the animal shoot out its viscid substance in rays and earn its living. Now the lowest types of Radiolaria are of this character. They have no shell or framework at all.
Observations conducted at Cuxhaven in 1839, had revealed the existence, at the surface of the waters of the Baltic, of living Diatoms and Radiolaria of the same species as those which, in a fossil state, constitute extensive rocks of tertiary age at Caltanisetta, Zante, and Oran, on the shores of the Mediterranean.
These silicious bodies belong partly to the lowly vegetable organisms which are called Diatomaceæ, and partly to the minute, and extremely simple, animals, termed Radiolaria. It is quite certain that these creatures do not live at the bottom of the ocean, but at its surface where they may be obtained in prodigious numbers by the use of a properly constructed net.
Such a colony would be admirable food for an early carnivore, and we soon find the protective principle making it less pleasant for the devourer. The first stage may be at least there are such Sponges even now that the common bed is strewn or sown with the cast shells of Radiolaria.
But if the Radiolaria and Diatoms are thus rained upon the bottom of the sea, from the superficial layer of its waters in which they pass their lives, it is obviously possible that the Globigerinoe may be similarly derived; and if they were so, it would be much more easy to understand how they obtain their supply of food than it is at present.
Darwin's great work have made their appearance. Professor Haeckel, to whom Schleicher addresses himself, previously took occasion, in his splendid monograph on the Radiolaria, to express his high appreciation of, and general concordance with, Mr. Darwin's views.
They are the minutest of the Radiolaria, which peopled in inconceivable multitudes the tertiary oceans; and, as they died, their minute skeletons fell down in a continuous rain upon the ocean bed, and became cemented into solid rock which geologic action has brought to the surface in Barbados and many other parts of the earth.
Thus, in the whole of the "intermediate zone," the silicious deposit which is being formed there, as elsewhere, by the accumulation of sponge- spicula, Radiolaria, and Diatoms, is obscured and overpowered by the immensely greater amount of calcareous sediment, which arises from the aggregation of the skeletons of dead Foraminifera.
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