the anatomy of the madreporaria. 13 



Note. 



For microscopic sections through both hard and soft parts of the 

 coral, such as are figured in (4) PI. XLL, Figs. 14, 15, I have found 

 the method, originally applied by von Koch to these forms, extremely 

 useful. The coral, having been left in borax carmine for three days, 

 and treated with acidulated alcohol for six hours, is transferred to 

 absolute alcohol, and from this to ether ; into the ether is dropped 

 absolutely dry powdered Canada balsam in small quantities at a time, 

 till enough is dissolved to make a block, rather larger when dry than 

 the specimen. The ether is driven off by a gentle heat, leaving the 

 coral permeated throughout by balsam. About a week should be 

 devoted to this part of the process. 



Sections are then cut with a lapidary wheel, or, if this is not 

 procurable, with a fret saw ; and ground like geological sections on 

 a slate, then polished on a water of Ayr stone. Oil and emery 

 powder should be avoided, water alone being used for the stones. 



One surface of the section having been ground and polished, it 

 should be affixed permanently by that surface to a glass slide, on to 

 which some dry Canada balsam has been melted, and not again be 

 moved. "When the other surface has been similarly ground and. 

 polished to the required thinness, it should be brushed lightly, first 

 with absolute alcohol, then immediately with oil of cloves ; this 

 removes all dirt from the surface. A drop of balsam in benzole 

 is then placed on the section, and the cover glass lightly dropped 

 on it. 



Erratum. 



In my previous paper (4) PI. XL., Fig. 1, the septa were wrongly 

 numbered ; they should have been marked 1, 4, 3, 4, 2, 4, 3, 4, 1, 

 reckoning on each side from the central " directive " septum, D. 



Literature. 



1. Milne-Edwards. — " Hist. Nat. d. Coralliaires," iii., p. 148. 



2. Yon Koch. — " Jen. Zeitschr.," Bd. xi. 



3. Moseley.— " Quart. Journ. Micr. Sci.," Oct., 1882. 



