196 Prof. P. M. Duncan on the Hard Structures of 



of tills laminate-and-pillar structure is readily understood after 

 the superficial structures of the colony, both on the upper and 

 lower surfaces, have been examined with care. On the upper 

 surface, and between the calices, are numbers of minute, 

 short, broad-based, sharply pointed spinules, placed rather 

 closely and arising from a perforated calcareous lamina, which 

 forms the outermost structure of the coraL 



By breaking away some part of this layer and its covering 

 of spinules a somewhat similar set of structures is to be seen 

 beneath, for the tops of small spinules, arising from a more 

 or less perforated surface, then become visible, and they are 

 evidently the relics of a former outer surface. Much cal^ 

 pareous matter has been, as a rule, added during development 

 to the outside of the old laminae and spinules, and their re- 

 lations to the existing outer structures is more or less hidden; 

 but on the lower surface of the coral the successive growth of 

 several lamina and spinules, one over the other, is plainly 

 exemplified, the resemblance of the under and the upper layers 

 being exact. 



The method of growth can be appreciated by examining the 

 surface of the coral beneath. There the spinules, in many 

 places, are enlarged at the top^ a calcareous tissue extending 

 on all sides from them, This tissue joins with that forming on 

 other spinulcSj and an imperfect and somewhat irregular lamina, 

 ^results and covers over the old surface and its spinules. 



The porosity of the lamina3 is due to the incomplete growth 

 of the calcareous film prising from the tops of the spinules ; 

 but it is lessened with age and calcareous deposition. The 

 corallites which have immersed calices must grow in length 

 in order to keep pace with the exogenous growth of the colony ;^ 

 but it is very ])robable that the simultaneous growth is in- 

 evitable and part of the necessary development, for there is 

 every reason to believe that the spinulation has to do with 

 the superficinl water-system common to the whole colony, and 

 \vhich detei'mines the symmetrical general growth. 



It was stated above that the walls of the corallites are well 

 developed, and it also appears that they are by no means 

 Jiighly perforated ^ on the contrary, the openings are few and 

 far between, and there are no large spaces by which buds can 

 communicate with the so-called parent, according to some 

 ideas. 



As in the former instance, the buds arise on the layer of 

 tissue surrounding the elder corallite, are developed out of the 

 superficial growth incident to exogenous growth, and have no 

 other communication with the interior of the previously exist- 

 ing corallite than the ordinary porosity. 



