MisceUaneona. 597 



individuals arise, solely at the expense of the oral disc and the 

 teutaouhir apparatus by fusion of its elements in pairs. 



If we imagine two contiguous tentacles in a state of semi- 

 expansion ; owing to their capitate form they come into slight 

 contact by their superior extremities and so define, between their 

 opposed faces and the portion of the buccal disc intercepted 

 between their two bases, a gutter, open interiorly on the side 

 of the mouth, exteriorly on the side of the margin of the 

 tentacular disc. If this arrangement be fixed by, so to speak, 

 solderiiig up the junction of the two surfaces which are in temporary 

 contact, the gutter aforesaid becomes a canal, which is at ouco 

 recognizable as the U-shaped canal. 



It is situate in au intertentacular plane, its two orifices open on 

 the oral disc, one on the outer side, the other on the inner of the 

 crown of tentacles ; lastly, the epithelial covering of its bore is 

 strictly ectodormic. 



lleturning to what has been described as the soldering together 

 of two tentacles, if we conceive it to be accompanied by the absorp- 

 tion of tlie two ectodermic surfaces along the line of which it has 

 taken place, it will in reality be effected through the intermediary 

 of their luesogleal lamella. We also note at the same time that 

 these two latter, fused into one, appear to continue, above the U- 

 shaped canal, the single mesogleal lamella of the subjacent mesentejv. 

 Now if we remove the special histological characters (nematocyst, 

 nervous system) from what is left of the ectoderm of the tentacles, 

 and give, on the other hand, to the cells of their endoderm the laro-e 

 size which is known to be the case, we have completed the synthesis 

 of a U-shaped organ without having supplied the normal polvpo 

 __^. with any elements other than those which we intended to employ. 

 *-' All that now remains is to make the absence of the U-shaped 

 canal-organ on the two partitions of the directing dorsal endoccele 

 agree with the apparent disposition of its tentacle. This latter, 

 not having experienced the fate of its neighbours, ought to be 

 recoverable. 



Its non-existence is, in fact, more apparent than real. A studv 

 of sections has enabled me to discover its presence in the gastro- 

 vascular cavity with ease. Invaginated in its endoccele, with its 

 short axial ectodermic canal opening on the buccal disc and its endo- 

 derm with its voluminous cells, it is in every sense comi)arable to its 

 homologue (dorsal tentacle) in the Oculininte. It is thus the totality 

 of the elements of the tentacular apparatus that the change affects 

 in Mudreiiora, while in Pcecilopora it affects but a small part (J), 

 and in Seriatopora and St^/IopJiora yV- 



The presence of like formations in creatures exhibiting such 

 differences of structure as the Oculininic and the Madreporina3 a 

 presence which renders their existence possible in all the Hexacorallids 

 under aspects which may otherwise vary between one group and the 

 other — the considerable development which they assume in those 

 individuals in which they are present, — causes one to suspect that 

 they must play an important rd/e in the physiology of these animals. 

 — ComptesRendns, tomecxxxviii. no. 24, pp. Ioll)-lo21 (13th June 

 1'J04'). 



