Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/398

 384 FORAMINIFERA The calcareous lamella of the Canadian Ophiealcite, which are always thickest near the base of the mass, are superposed one upon another so as to include between them a succession of &quot;stories &quot; of chambers (fig. 34, A 1, A 1 , A 12 , A 2 ), the chambers of each &quot; story &quot; FIG. 34. Calcareous skeleton of Eozoon canadense: A 1, A 1 , chambers of lower story ; A 2 , A 2 , chambers of upper,story, imperfectly divided at a, a ; n, B, tubulated or Nummuline layers ; c c, intermediate skeleton; D, large passage from one story to another; E, E, E, branching canal-systems. opening one into the other, as at ft, a, like apartments en suite, but being occasionally divided by complete septa, as at b, b, which arc traversed by passages of communication between the chambers they separate. Each layer of shell consists of two finely-tubulated or Nummuline &quot; lamella}, B, B, which form the boundaries of the chambers above and beneath, and of an intervening deposit of homogeneous shell-substance, c, c, which constitutes the &quot;inter mediate skeleton.&quot; The amount of this varies considerably in dif ferent layers, while the thickness of the &quot; proper wall &quot; of the chambers (or &quot;Nummuline lamella&quot;) remains almost constant, the distinction between the two being just as marked (in well-pre served specimens) as it is in the recent Calcarina (fig. 19). The tubuli or the &quot;Nummuline&quot; lamelke are usually filled up (as in the Nummulites of Nummulitic Limestone) by mineral infiltration, so as to present only a fibrous appearance in thin transparent sec tions ; but it fortunately happens that, through its having escaped such infiltration, the tubulation (fig. 35, n, a) is occasionally as distinct as it is in recent Nummuliue shells, bearing a strong resemblance in its occasional waviness (as at a, a ) to that a crab s claw. The &quot; intermediate skeleton,&quot; whenever it forms a thick layer, is penetrated by arborescent systems of canals (fig. 34, E, E), which are often distributed so extensively and so minutely through its substance as to leave very little of it without a branch. These FIG. &amp;lt;!&quot;). Highly-magnified section of a portion of the calcareous skeleton of Eozoon canatlense : a, a, Nummuline layer showing parallel tubuli with a wavy bend along the plane, a ; b, origins of canal-system penetrating the . intermediate skeleton c, c, which is traversed obliquely by cleavage-planes that . pass on into the Nummuline layer. canals (fig. 35, b, b) take their origin, not directly from the chambers, but from irregular lacuna; or interspaces between the outside of the proper chamber-walls and the &quot;intermediate skeleton,&quot; exactly as in Calcarina, the extensions of the sarcode-body which occupied the most characteristic specimens of Eozoic structure. On the other hand, the late Professor Max Sclmltze, who took up the enquiry towards the end of his life, not only publicly and most explicitly expressed his conviction that the canal-system found in the calcareous lamella; must be organic, but left behind him an elaborate Memoir on the subject, with ample illustrations, which unfortunately still remains unpublished. them having apparently been formed by the coalescence of the pseudopodial filaments which had issued forth through the tubulated lamellse. It is to be remarked that the substance, not merely of the intermediate skeleton, but of the Nummuline layer, is traversed by oblicpue lines, indicating the cleavage-planes of calcite. This is what is constantly seen in fossilized calcareous organisms such as the shells and spines of Echinida, or the stems of Crinoidca which retain their organic arrangement unchanged, and thus affords no basis whatever for the contention that these calcareous layers are purely mineral. On the other hand, the fact that the portions of the canal-system, shown in thin sections (fig. 35), continually cross the cleavage planes, instead of lying between them, furnishes a strong objection to the hypothesis that the appearances which have been interpreted as indicating a regular distribution of ramifying canals canhavebeen produced by mineral infiltration. Further, the distinct continuity of these cleavage-lines through the &quot;Nummuline layer &quot; (fig. 35, a, a) proves this layer to be essentially calcarcmis, the layer of serpentine-fibres which is commonly found in its place after de- calcification being a secondary deposit, formed in the manner to be presently described. When a well-preserved fragment of Eozoon has been treated with dilute acid, so as to dissolve away the calcareous lamella, we have an &quot; internal cast &quot; in serpentine, which gives us a precise model of the sarcodic body by which the cavities of the calcareous struc ture were originally occupied. We see, in the first place (fig. 36), FIG. 36. Internal cast, in Serpentine, of the animal body of Eozoon canademe,. that each of the layers of serpentine forming the lower part of such a specimen shows more or less of a segmental arrangement, being, in fact, made up by the coalescence of a number of minute serpen- tinous granules, such as are shown separately or but slightly coales cing in the upper part of the figure. This shows that there is not that difference between the regularly &quot; lamcllated &quot; and the &quot;acervuline &quot; plans of growth which might at first sight be sup posed, the chambers having been separate in the latter, whilst in the former they constituted imperfectly subdivided galleries. In those wider spaces between the serpentine-layers, which were origin ally occupied by the thicker calcareous layers forming the &quot;intermediate skeleton,&quot; we find internal casts of the branching canal-system ; and the development of this system is found, as in recent Foraminifcra, to bear a constant relation to the amount of the secondary calcareous deposit. But further, in specimens in which the &quot; Nummuline&quot; layer was originally well preserved, and in which the decalcifying process has been carefully managed, that layer is represented by a thin white film covering the exposed surfaces of the segments ; as is shown superficially over the upper part of fig. 36, and in section, along the margins of the serpentine layers, in the lower. When this film is examined with a sufficient magnifying power, it is found to consist of extremely minute needle-like fibres of serpentine ; which sometimes stand upright, parallel, and almost in contact with one another, like the fibres of asbestos, but which are frequently grouped in converging brush-like bundles, so as to be very close to each other in certain spots at the surface of the film, whilst widely separated in others, thus indicating exactly the same irregularities in the grouping of the tubuli that (as already men tioned) we find in recent Nummulines. And it is not unfrequcntly seen that where bundles of these fibres converge towards the surface, so that the pseudopodial threads they represent would have issued forth in clusters, the internal casts of the canal-system take their origin in such aggregations. We have here, in fact, in this most ancient of all fossils at present known, the most complete model wo possess of any extinct animal, extending even to its soft sarcodic, threads of less than T TiVu7&amp;gt;th of an inch in diaineter, this model being conformable in all essential particulars to the &quot; internal casts&quot; of existing Foraminifcra which are at present in course of produc tion on the sea-bottom. Geographical Distribution. M ost of the Families of this group have a very wide geographical distribution, this