ALVEOLINA 



80S 



especially [abundant in those of some of the Philippine Islands, of the 

 Red Sea, of the Mediterranean, and especially of the JEgean. When 

 such discs are subjected to microscopic examination, they are found 

 (if uninjured by abrasion) to present the structure represented in 

 fig. 609, where we see on the surface (by incident light) a number 



s, 



a 



i 

 | 



J 



s" 



i 



of rounded elevations, arranged in concentric zones around a sort of 

 nucleus (which has been laid open in the figure to show its internal 

 structure) ; whilst at the margin we observe a row of rounded pro- 

 jections with a single aperture or pore in each of the intervening 

 depressions. In very thin discs the structure may often be brought 

 into view by mounting them in Canada balsam and transmitting 



