'38 



protoplasm (fig. 3;. As the edges of the septa are approached 

 the layer thickens. Nuclei become more frequent, and tend 

 to exhibit a definite network. The protoplasm forms, as it 

 were, two layers, the one against the structureless lamella,, 

 the other with a ragged edge against the corallum, joined by 

 a series of bridges between large vacuoles. The nuclei com- 

 monly lie in the outer layer or in these bridges (fig. i). At 

 the edge of the septum the ectoderm is still thicker, but the 

 large vacuoles are nearly absent, and towards the outer side 

 [i.e.., against the septum^ the protoplasm is almost hyaline. 

 The same, too, is the case at the upper edge of the epitheca,. 

 where the ectoderm forms practically a thick hyaline pad, 

 seated on the corallum. 



The calicoblastic ectoderm is also thickened greatly, where 

 the mesenteries are attached to the corallum and on each side 

 of the same (fig. 2). Its edge against the corallum is very 

 ill-defined, indeed ragged and broken. The protoplasm is 

 densely granular, often with relatively large granules. The 

 processes which attach the structureless lamella to the 

 corallum (desmocytes) do not materially differ from what 

 Bourne, Fowler and others have described. They are 

 especially well developed at the attachments of the mesenteries 

 (fig. 2), but may occur in any part, small bunches being in 

 particular scattered over the septal sides. Their development 

 was quite clear, and did not differ materially from Bourne's 

 description.^ The first appearance of any desmocytc could be 

 seen in a granular mass of protoplasm against the corallum, 

 to which from the first it seemed to be attached. Subsequently 

 by growth inwards it joins the structureless lamella, which 

 may be thickened so as to meet it. At its base or side is 

 always a nucleus with a well-defined network, but otherwise 

 the same as those of the layer. 



My researches add little to Bourne's most admirable and 

 lucid account of the formation of the skeleton. There are no 

 " scales," '"■ nor is there any indication of the possible forma- 

 tion and shedding of any such. The appearance of the layer 

 in a few preparations of both hard and soft parts only showed 

 that the structure in the decalcified sections had in no way 

 changed. The layer had in all cases become slightly 

 separated from the corallum — perhaps by killing — except 

 where the desmocytes attached themselves. 



The thickening of the ectoderm on the septal edges was 

 found everywhere, but it varied enormously, at intervals being 

 extremely thick and much more hyaline. Where secretion 



r. Quart., Jour. Micro. Set., vol. 41, pp. 499-54? ('899)- 



2. P'ide " Microscopic and Systematic Study of Madreporarian Types of Corals, "^ 

 by Maria M. Ogilvie, Phfl. Tram. li.S., vol. CLXXXVJI., p. 83 (1896). 



