THE ASTRORIIIZiE. 55 



in Stromatopora discoidea, Lonsd., is that we get very different appearances in thin 

 sections to those presented by the normal Stromatoporce. Thus, in tangential sec- 

 tions (Plate VII, fig. 1) the grooves representing the astrorhizal canals are seen to 

 be constant in form and position at whatever level in the " latilamina " the section 

 may have been taken. In vertical sections, further, we do not see the round 

 apertures representing the cut ends of the radiatiug astrorhizal canals, but in place 

 of these we observe (Plate VII, fig. 2) deep vertical fissures, which are in many 

 places crossed by transverse " tabula?," and which clearly represent, in large part 

 at any rate, the zooidal tubes. 



In those Stromatoporoids which possess astrorhiza?, there arises an important 

 distinction according as the astrorhizal of successive lamina? are produced irre- 

 gularly, or are developed one above the other in a system of vertically superposed 

 groups. In the latter case, the astrorhiza? of each vertical series are connected 

 together by an approximately vertical central tube, which opens on the surface of 

 the ccenosteum by a distinct aperture, from which the grooves of the last-formed 

 astrorhiza radiate (Plate HI, figs. 4 and 6, and Plate IV, fig. G). The opening of 

 this central canal is often placed on a more or less conspicuous " monticule," and 

 Bargatzky conjectures that the existence of such monticules or " warts " may be 

 taken as a general indication of the presence of vertically superimposed astrorhiza?. 

 Prof. Ferd. Roemer has doubted the existence of such vertical central canals 

 to the astrorhizal groups, and has explained the phenomena presented by these as 

 being really produced, in a manner formerly alluded to, by the inclusion of the 

 tubes of Sjurorbis in the tissues of the growing Stromatoporoid. An examination 

 of thin sections, however, shows this supposition to be baseless, though such 

 imbedded Spirorbcs do occur not infrequently. Thin sections, in fact, entirely con- 

 firm the conclusion which one would naturally draw from the regular distribution 

 of these prominent apertures on the surface of many Stromatoporoids (see Plate 

 III, figs. 4 and 6) — the conclusion, namely, that they are the apertures of canals 

 belonging to the ccenosteum itself. These axial canals of the astrorhiza? are wholly 

 devoid of proper walls, as is also the case with the radiating canals of the astro- 

 rhiza?, and they cannot, therefore, be confounded with the wholly different walled, 

 tubes of the so-called Caunoporce. As regards their function, we may suppose that 

 these axial astrorhizal canals lodged primary stolons of the ccenosarc, from which 

 were given off the radiating and inosculating stolons occupying the grooves of the 

 astrorhiza?. There does not seem, certainly, to be any ground for regarding these 

 canals as having served for the lodgment of zooids. 



Certain types of Stromatoporoids are apparently wholly destitute of astrorhiza?. 

 I have, for example, failed to detect any definite representatives of these structures 

 in any species of Labechla. Other types, again, appear to constantly possess these 

 structures. They are, in fact, present in so many Stromatoporoids, of the most 



