358 Messrs. R. G. Nelson anl P. M. Duncan on the 



taken of it under advantageous circumstances. For many 

 years these drawings have been on the point of being pub- 

 lished, and now, owing to their manifest importance, they are 

 brought forward. In the mean time, and especially of late 

 years, since the Tabulata were considered in the Keport to the 

 British Association already noticed, the other contributor to 

 this paper has microscopically examined many specimens, and 

 has worked up to the point where Lieut, (now Major-General) 

 Nelson's long-completed work began. 



There is little to add to the description of the hard parts, 

 except to notice that all are agreed in their construction, and 

 that the tubular nature of the coenenchyma relates to old polyp- 

 calices in long series, the tabulaB having been absorbed or 

 broken down. The reticulate appearance on the surface is pro- 

 duced by well-marked ridges and depressions ; and cavities exist 

 below the surface in this reticulate mass, which are connected 

 with the calicular spaces. The tissue soon becomes hard and 

 more solid with depth ; and infiltration of carbonate of lime 

 appears to have united the reticulate sclerenchymatous pro- 

 cesses. But in the midst of branches the reticulate and 

 apparently cellular arrangement persists. The sclerenchyma 

 consists of fibrous-looking plain spicula, arranged side by side 

 and above each other ; there are also homogeneous carbonate 

 of lime and granules. The soft tissues (or rather the organic 

 basis which permeates the coral, and in and about which the 

 calcareous element is deposited) are much more plentiful than 

 might be expected ; they can be got out by weak hydrochloric 

 acid (dilute), and evidently line the calicular fossae, the top of 

 the tabulffi, and enter into the cavities in the reticulate super- 

 ficial structure. The shape of the solid parts of the reticulation 

 is retained by this means, sometimes veiy perfectly. Once 

 only was a glimpse obtained of any thing like a polyp ; and 

 it foreshadowed the truth long before obtained at the Bermudas. 



The polyp of Millepora alcico mis, a.s seen by one of us at 

 Bermuda in full expansion, is a very remarkable one ; and it is a 

 great satisfaction to be able to state that L. Agassiz saw only a 

 part of the whole, and came to his conclusions too rapidly. The 

 polyps are of different lengths according to their growth, are 

 slender, and stand erect in crowds around the branches (fig. 2). 

 Each arises from a cylindrical stem, which is rendered slightly 

 square close to four tentacles which project upwards and out- 

 wards. Their tips are swollen and rounded ; and their bases 

 are continuous by means of straight disk tissue which overlaps 

 slightly the analogue of the oral opening. Out of this open- 

 ing comes a second cylinder, to terminate in four other tentacles 

 in tlie same way ; and in some polyps there is a further growth 5 

 so tliat there are two or more rows of tentacles separated 



