Study of Madreporarian Tyyes of Corals. 219 



XXX. — Microscopic and Systematic Study of Madreporarian 

 Types of Corals. Bj Maria M. Ogilvie, D.Sc* 



In the first part of this paper the author gives the results of 

 her microscopic investigations on the structure of the skeleton 

 in a number of typical Madreporaria. 



Detailed microscopic study of the surface of the septum 

 showed small scales lying above and against one another, 

 somewhat like the slates of a roof, and consisting solely of 

 fine, pjirallel-placed, or diverging aragonite fibres. Besides 

 these calcareous scales^ ectodermal cells (calicoblasts) could 

 still be observed in several cases attached to the surfaces of 

 septa in fresh specimens. Heider and one or two other 

 authors have already mentioned the frequent occurrence of 

 organic polypal remnants on skeletal surfaces. 



The scales observed by the author were found to agree 

 precisely in shape and size with the calicoblasts, and to show 

 various transitional stages from the organic cell to the calcified. 

 It follows from this that the skeleton of Madreporaria takes 

 its origin from an actual calcification of the calicoblasts, and 

 not, as Koch thought, by a secretion laid down outside the 

 cells. The author found further that the calcareous scales 

 were arranged in extremely thin lamellae, and that the fibro- 

 crystalline deposit was similarly oriented in successive 

 lamellse. 



The stages in the process of skeleton-building may be thus 

 generally stated : — 



(1) Calcareous deposit is laid down within individual 

 calicoblasts of the ectoderm. At the same time new ecto- 

 dermal cells are formed next the mesogloea, and these which 

 are undei going calcification become loose external layers of 

 partly calcareous, partly organic tissue. 



(2) Fibro-crystalline groups of aragonite are built up in 

 the individual cells, and the cell-walls shrivel. Thus a 

 connected calcareous lamella is formed, which is ultimately 

 incorporated with the skeleton. 



(3) Changes of disintegration and crystallization still con- 

 tinue after the cell- lamella has severed living contact with 

 the polyp. The disintegration of organic cell-remnants 

 produces various flecks and bands, usually carbonaceous, in 

 the midst of the crystalline deposit. These afford the 



* From the ' Proceedings of the Royal Society,' vol. lix. no. 353, 

 pp. 9-18 ; being an abstract of a communication received July 24, 18i)5. 



15* 



