Structure 0/ Stromatopora. 261 



which the stoloniferous tubulation is afterwards to be lodged, 

 but which, disappearing in the dried state, leave the latter in 

 the form so beautifully displayed in the surface of the branched 

 species of Hydractinia (H. arborescens, Ann. 1878, vol. i. 

 p. 298, pi. xvii. fig. 4). The same kind of grooved venation 

 exists in Miilepora alcicornis either in the surface or immedi- 

 ately beneath the last or outer layer, according to the degree 

 of development to which the layer has arrived, since, as may 

 be gathered from what has been stated of the stoloniferous 

 tubulation in Hydractinia, the tubulation soon obscures itself 

 by the development of the polypary around and above it. 

 The same grooved venation may be beautifully seen on the 

 surface of the fossil species, viz. Hydractinia pliocena, All- 

 man, = Stromatopora mcrustans, Goldfuss, ut antea, and not 

 only on the surface but in the subjacent layers as they are 

 split off from the fossilized polypary or corallum. 



Now no naturalist or comparative anatomist (for it is essen- 

 tial that a palasontologist should be one) could ever confound 

 this structure with that of the excretory canal-system of 

 sponges, however like the latter may be to it ; if so, I must 

 refer him to Mr. Moseley's description of it in the living- 

 species under the name of " hydrophyton " (Phil. Trans. 

 1877, vol. clxvii. p. 125, pi. iii. fig. 16, &c), wherein it will 

 be found to be " lined, and in many places filled with cellular 

 elements " (p. 128, pi. iii. fig. 17), and not hollow like the 

 canal of sponges ; while I myself cannot see any difference, 

 except in form, between this grooved venation and the stellate 

 venation — which in the lapidified state of Stromatopora in the 

 horizontal section is filled Avith transparent calcite, but which, 

 of course, when in the interior of the corallum becomes tubu- 

 lar, and in the larger forms of Pit-Park Quarry, to which 

 I have alluded, filled (when under decomposition) with a 

 mould of opaque white calcite, following the same mineral 

 changes as before mentioned under similar circumstances, 

 and thus contrasting strongly, in its branching form, with the 

 dark remains of the decomposed corallum in which it is thus 

 imbedded. 



Nature frequently repeats herself in form, although not in 

 function, as if there were a unity of design. Thus there is a 

 specimen of a polyzoon in the Liverpool Free Museum, which 

 was brought to my notice by Mr. T. H. Higgin, F.L.S., 

 where the cceuobium is identical with the general form of the 

 siliceous hexactincllid sponge called Eurcte farreopsis. which 

 I have figured in the ' Annals ' (vol. xix. pi. ix. fig. 1) ; and 

 I possess the calcareous cormus of a Synascidian still larger, 



