594 ANATOMY OF NEOHELIA POECELLAXA (mOSELEy). 



There is really very little doubt that the horny substance is secreted by the 

 Neohelia itself, for it is in a thin continuous layer, and conforms in outline with the 

 calcareous skeleton, and, like it, is interrupted at the apertures in the wall of the 

 tube. If the horny membrane were secreted by another animal, we should not expect 

 to find these poral interruptions, and we should expect to find some trace of the 

 animal which formed it. 



In the Alcyonaria and among the Zoantharia — the Actiniaria and the Antipa- 

 tharia — there are many instances of the secretion of a horny substance, therefore, it is 

 not improbable that such may occur among the Madreporaria. The layer of horn lies 

 in contiguit}" with the calcareous skeleton, and I have not observed any aggregation 

 of cells between the homy substance and the skeleton b}" which the former could be 

 secreted, but it is possible that it may be secreted by the epithelial layer, in a 

 manner similar to the secretion of the calcareous Epitheca by the Randplatte in a 

 form like Caryophyllia. 



It is probable that the young coral polyp after settling down, has the power of 

 secreting, not onlj' a skeleton of lime but also a homy substance as in the Gorgonids. 

 As the 3"oung coral grows, it tends to encrust the object to which it has affixed 

 itself. This it would do in a more or less irregular manner, leaving gaps here and 

 there, — the apertures to which I have referred. As growth proceeds, the holes 

 become filled in until they are finally obliterated. (Compare Moseley's figures ^vith 

 Fig. 1.) 



Among the Alcyonaria, there are two nearly allied genera, Suheria and Soleno- 

 caidon (2.5) belonging to the family Briareidae which show certain similarities as 

 regards their manner of growth with the genus Neohelia. Wright and Studer say of 

 Suheria gentJm, " The colony forms at first an encrusting surface over the long denuded 

 stems of a Gorc/onia. On reaching the termination of the foreign axis, and on several 

 occasions at intervals along its length, little upright stems arise, sometimes simple, but 

 sometimes branched." 



In the case of Neohelia, I have seen two specimens, one (Moseley's) encrusting 

 a Gorgonid stem, the other erect and free but the base missing. It is probable that 

 the colony begins by encrusting a Gorgonid stem and afterwards sends off free branches. 

 Our specimen is probably one of the free branches. 



The genus Solenocaulon (25 and 20) allied to Suberiu is characterised by the 

 tubular form of the axis which is perforated as in Neohelia, the tubes being formed 

 of a thin coriaceous substance. Gray says of it, " The coral cannot be considered as 

 a solid stem becoming hollow, as the last formed (younger) parts at the ends of the 

 branches are in the form of a foliaceous expansion, which gradually folds up together 

 on itself, coalesces and forms a tube nearly of the same diameter as the main stem. 

 The large apertures which occur in the stem and base of the branches, and communi- 

 cate with the central cavity are the parts of the expanded lamina which have not 

 been closed in when the other portions of the tube were formed." It is very probable 

 that the tube of Neohelia is formed in like manner, if so, then the apertures are 

 analogous, i.e. the holes in the wall of the tube of Neohelia are spaces which have 

 not been filled in by the peritheca. 



