CALOAREOUS SKELETON OF THE ANTHOZOA. 537 



lamella consists of strands of crystalline fibres which have a 

 general direction parallel with the long axis of the spicule. I 

 cannot say exactly how this arrangement was brought about, 

 but it certainly is not due to the apposition of calcified cells, 

 for the whole spicule was formed inside a cell or coenocyte, and 

 was covered in all- stages of its growth by a spicular sheath 

 of organic matter. In fact, the spicule was, from its early 

 origin, separated from the protoplasm which elaborated the 

 material necessary for its further growth by a layer of some 

 cuticular material. 



The case in the Madreporaria, and also in Heliopora, 

 appears to be somewhat parallel. Fig. 19 shows that in 

 Heliopora a cuticular external limiting membrane extends from 

 the edges of the desmocyte over the adjoining calicoblasts. 

 Figs. 27, 33, and 43 show the same phenomenon in Madre- 

 poraria. And there are numerous indications in flat prepara- 

 tions that the calicoblast layer both in Heliopora and 

 Madreporaria is separated by an external limiting membrane 

 from the corallum. I have frequently noticed at the edges of 

 the septa of Caryophyllia that there was a space between the 

 edge of the corallum and the overlying soft tissues, and that 

 this space was occupied by a colloid substance in which minute 

 particles could be detected. I was for a long time doubtful 

 whether this appearance was deceptive or not, but studies of the 

 growth of costal spines in sections through hard and soft parts 

 of the different species of Madrepora named above have settled 

 the question. 



Fig. 43 represents a costal spine with its adherent tissues in 

 M. subulata. At the bottom of the figure is a dark '' centre 

 of calcification," from which lines, representing fibro-crystals, 

 diverge to the surfaces of the spine. At the tip of the spine 

 its contours become indefinite, and instead of the compact 

 crystalline arrangement we have separate diverging fibres, and 

 outside of these, minute particles which show a tendency to 

 arrange themselves in lines. At the base of the spine calico- 

 blasts^'may be seen lying close to the corallum. Towards the 

 apex of the spine they no longer lie close to the calcareous 



