26 MR. H. N. MOSELEY ON SOME CORALS. [Jan. 20, 



layer of the body- wall of the animal, but that it is a secondary struc- 

 ture formed within the body-cavity by the gradual coalescence of the 

 outer extremities of the calcareous septa. In this conclusion be is 

 supported by the fact that in transverse sections of the coral-wali of 

 many species of corals suture-like lines are to be made out, separating 

 the calcareous tissue composing it into a series of masses which are 

 apparently nothing else than the swollen peripheral portions of the 

 septa themselves. 



" Dr. Koch, in a paper on the skeleton of corals, lately published 

 in ' the Morphologisches Jahrbuch'', exhibits his results in three 

 diagrams. The diagrams represent sections of the same coral, a Caryo- 

 phyllia, at various heights, and are believed by the author to exhibit 

 also the process by which the actual development of the hard 

 skeleton or corallum takes place. In the first the septa are seen quite 

 separate from one another and occupying the centres of the inter- 

 mesenterial spaces. In the second, the septa have coalesced by means 

 of lateral outgrowths, and a complete calcareous wall is formed with 

 the continuations of the mesenteries and intermeseuterial spaces be- 

 yond it, these being shown much larger than in nature for the sake 

 of clearness. In the third section, taken towards the bottom of the 

 cups, the tissues external to the calcareous wall have perished and dis- 

 appeared — this perishing of the lower parts of the soft tissues on the 

 outside of the coral's cup at its base as growth proceeds at the sum- 

 mit being a normal process in the case of many corals, but not by any 

 means in all. 



" The calcareous parts are covered everywhere, both according to 

 Dr. von Koch's observations and my own and those of other inves- 

 tigators, with a layer of mesodermal tissue, within the substance of 

 which doubtless they are deposited. 



" It will be seen that the outer chambers and mesenteries are found 

 by Dr. von Koch to exist only in the upper part of the coral. In 

 his first diagram there is nothing to be seen but what would have 

 been expected : the exsert calcareous septa rise above the wall of the 

 coral-cup ; and thence they only are cut across in a superficial section. 

 In order to explain what is seen in the second section, it may possibly 

 not be necessary to assume that the soft tissues in which the calca- 

 reous wall is embedded do not belong to the wall of the animal. What 

 seems to be the case is that the intermeseuterial cavities lap over a 

 short distance beyond the edge of the coral-cup, and are thus exposed 

 in section beyond it when the entire coral is cut across. The soft 

 tissues of the disk are to be seen in a living expanded Caryophyllia 

 rising far above the summit of the corallum. No doubt, in specimens 

 preserved in alcohol, the tissues are drawu down to a certain abnor- 

 mal extent on the outside of the corallum as well as into its interior by 

 contraction. The soft tissues in which the calcareous wall is deve- 

 loped may perhaps still be regarded as derived from the body-wall, 

 although they do not quite coincide with the outer portion of it to- 

 wards the summit of full-grown corals. In many simple corals the 



' " Bemerkungen iiber das Skelet der Korallen," Morph. Jahrbuch, Bd. t. 

 p. 316. 



