MINUTE STRUCTURE. 37 



system of minute branching tubnli. Thus, in Stromatoporella granulata, Nich., 

 from the Hamilton formation of Canada, in which the skeleton has undergone little 

 change, tangential sections (Plate I, fig. 4) show that the skeleton-fibre is traversed 

 by numerous minute vesicular cavities and elongated or flexuous canaliculi, 

 separated by the ordinary granular tissue of the skeleton. Vertical sections (Plato 

 I, fig. 5) exhibit the same condition of things, the minute channels of the fibre 

 being mostly directed vertically, and leaving a comparatively clear central line in 

 the centre of the fibre. The same structure is still better shown in other species of 

 Stromatoporella. Thus in S. eifeliensis, Nich. (Plate XI, figs. 1 and 2), both the 

 horizontal laminae and the radial pillars are seen in really well-preserved examples 

 to be traversed by a central clear space, connected on both sides with a complex 

 system of ramifying canaliculi, which branch out in the substance of the fibre. 

 There seems no reason to doubt that the clear central line above spoken of is really 

 a tube, and that the entire system is one of minute intra-skeletal tubuli filled 

 during life with living matter, similar to what is found in the skeleton of the 

 living Distichopora (Plate IV, fig. 4, and Plate IX, fig. 5). A system of precisely 

 similar tubuli is found in an allied species of Stromatoporella from the Eifel (Plate 

 XI, figs. 3 and 4). On the other hand, in S. (Diapora) laminata, Barg., the 

 skeleton-fibre has more of a coarsely porous than of a tubulated structure (Plate XI, 

 fig. 10), tangential sections of this species often showing here and there compara- 

 tively large-sized clear circular spaces, which seemingly represent the axial canals 

 of the radial pillars. 



The cases just considered are alike in the fact that the skeleton-fibre, as seen 

 in thin sections, is opaque and granular, while the pores or tubuli appear as clear 

 spaces in the substance of the fibre. There are cases, however, in which this state 

 of things is reversed. This is seen on a large scale in the genus Her •mato stroma, 

 in which the skeleton-fibre is composed of clear and transparent carbonate of lime, 

 exhibiting in its interior conspicuous opaque dots and lines. In vertical sections 

 (Plate III, fig. 2) each radial pillar exhibits a dark central axis, while similar but 

 more slender lines run in the interior of the horizontal larnince. In tangential 

 sections (Plate III, fig. 1) each transversely-divided radial pillar exhibits a central 

 dark dot, from which often radiate delicate dark lines. It is hardly possible that 

 we can here have anything else to deal with than a more or less complicated canal- 

 system in the interior of the skeleton-fibre, the larger divisions of which are now 

 injected with some opaque material, such as oxide of iron. 



The same phenomenon on a more minute scale, and in a completely convincing 

 form, is shown by specimens of Stachyodes verticillata, M'Coy, sp. In some 

 examples, namely, of this species the skeleton-fibre is traversed by delicate tubuli, 

 which appear in cross sections as transparent dots (Plate XI, fig. 6), and in 

 longitudinal sections as clear lines. In other specimens of the same species no 



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