Now if we regard these structures as those of an infiltrated fossil, as described in last chapter, their interpretation will not be difficult. The original organism was composed of calcareous matter in thin concentric laminæ, connected with each other by pillars and plates of similar material. Between these laminæ was lodged the soft, jelly-like substance of a marine animal, growing by the addition of successive layers, each protected by a thin calcareous crust. The layers were originally traversed by very numerous parallel tubuli, permitting the soft protoplasm to penetrate them; and when, in the progress of growth, it was necessary to strengthen these layers, they were thickened by a supplemental deposit traversed by larger and ramifying canals. When the animal was dead, and its soft parts removed by decay, the chambers between the laminæ, as well as the minute canals and tubuli, became infiltrated with mineral matter, in the manner described in the last chapter, and when so preserved became absolutely imperishable under any circumstances short of absolute fusion. [Illustration: FIG. 17.—Magnified group of canals in supplemental skeleton of _Eozoon_. Taken from the specimen in which they were first recognised (_Life’s Dawn on Earth_).] [Illustration: FIG. 18.—Portion of _Eozoon_ magnified 100 diameters, showing the original cell-wall with tubulation, and the supplemental skeleton with canals.—After Carpenter. _a_, Original tubulated wall or “Nummuline layer.” More magnified in Fig. A. _b_, _c_, Intermediate skeleton, with canals.] This interpretation leads to the conclusion, at which I arrived from the study of the first well-preserved specimen ever submitted to microscopic examination, that the animal which produced the calcareous skeleton of _Eozoon_ was a member of that lowest grade of Protozoa known as Foraminifera; and which, after living through the whole of geological time, still abound in the sea. The main differences are, that _Eozoon_ presents a somewhat generalised structure, intermediate between two modern types, and that it attained to a gigantic size compared with most of these organisms in later periods. How near it approaches in structure to some modern forms may be seen by comparison of the recent species represented in Fig. 19, in which the parts corresponding to the chambers, laminæ, tubuli, and canals of _Eozoon_ can be readily distinguished. [Illustration: FIG. 19.—Magnified portion of shell of _Calcarina_.—After Carpenter. _a_, Cells. _b_, Original cell-wall with tubuli. _c_, Supplementary skeleton with canals.]