. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. 70 HISTORICAL The concentrically-laminated mass of Eozobn is composed of numerous calcareous layers, representing the original skele- ton of the organism (fig. 23, h). These calcareous layers serve to separate and de- fine a series of cham- bers arranged in suc- cessive tiers, one above the other (fig. 23, A, B, C); and they are perjforated not only by passages (fig. 23, r), which serve to place suc- cessive tiers of cham- bers in commun
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. 70 HISTORICAL The concentrically-laminated mass of Eozobn is composed of numerous calcareous layers, representing the original skele- ton of the organism (fig. 23, h). These calcareous layers serve to separate and de- fine a series of cham- bers arranged in suc- cessive tiers, one above the other (fig. 23, A, B, C); and they are perjforated not only by passages (fig. 23, r), which serve to place suc- cessive tiers of cham- bers in communica- tion, but also by a system of delicate branching canals (fig. 23, d). Moreover, the central and prin- cipal portion of each calcareous layer, with the ramified canal- system just spoken of, is bounded both above and below by a thin lamina which has a structure of its own, and which may be regarded as the proper shell-wall (fig. 23, a a). This proper wall forms the actual lin- ing of the chambers, as well as the outer surface of the whole mass; and it is perforated with numerous fine vertical tubes (fig. 24, a a), opening into the chambers and on to the sur- face by corresponding fine pores. From the resemblance of this tubulated layer to similar structures in the shell of the Nummulite, it is often spoken of as the " Nummuline ; The chambers are sometimes piled up one above the other in an irregular manner; but they are more commonly arranged in regular tiers, the separate chambers being marked ofi" from one another by projections of the wall in the form of parti- tions, which are so far imperfect as to allow of a free communi- cation between contiguous chambers. In the original condi- tion of the organism, all these chambers, of course, must have been filled with living matter; but they are found in the present state of the fossil to be generally filled with some silicate, such as serpentine, which not only fills the actual chambers, but has also pene
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