It has been pretended that the veins of chrysotile, when parallel to the laminæ, cannot be distinguished from the minute tubuli terminating on the surfaces of the laminæ. I feel confident, however, that no microscopist who has seen both, under proper conditions of preservation and study, could confound them. The fibres of chrysotile are closely appressed parallel prisms, with the optical properties of serpentine. The best preserved specimens of the "proper wall" contain no serpentine, but are composed of calcite with extremely minute parallel cylinders of dolomite about five to ten microms. in diameter, and separated by spaces greater than their own diameter (Figs. 40, 41). In the rare cases where the cylinders are filled with serpentine, they are, of course, still more distinct and beautiful. At the same time, I do not doubt that observers who have not seen the true tubulation may have been misled by chrysotile veins when these fringe the laminæ. Möbius, for instance, figures the true and false structure as if they were the same. [Illustration: Fig. 40.--_Cross section of similar Tubuli to those in Fig. 39, more highly magnified, and showing granular character of the test._ (From camera tracings.)] [Illustration: Fig. 41.--_Comparison of Tubulate Wall and Prisms of Chrysotile in perspective._] [Illustration: _Canals of Eozoon._ (After Möbius.)] [Illustration: _Finer Canals of Eozoon._ (After Möbius.)] [Illustration: _Canals of modern Calcarina._ (After Carpenter.)] [Illustration: _Canals and Tubule of Tertiary Nummulina._ (After Möbius.)] Fig. 42. Figures selected from Möbius, to show the resemblance of structures of Eozoon to those of modern Foraminifera. Protest should here be made against that mode of treating ancient fossils which regards the most obscure or defaced specimens as typical, and those better preserved as mere accidents, of mineral structure. In Tertiary Nummulites injected with glauconite it is rare to find the tubuli perfectly filled, except in tufts here and there; yet no one doubts that these patches represent a continuous structure. I have remarked on previous occasions that the calcite constituting the laminæ of Eozoon often has a minutely granular appearance, different from that of the surrounding limestone. Under a high power it resolves itself into extremely minute dots or flocculi, somewhat uniformly diffused. Whether these dots are particles of carbon, iron, apatite, or silicious matter, or the remains of a porous structure, I do not know; but similar appearances occur in the calcareous fossils contained in altered limestones of later date. Wherever they occur in crystalline limestones, supposed to be organic, the microscopist should examine them with care. I have sometimes by this appearance detected fragments of Eozoon which afterward revealed their canals.