14 G. HERBERT FOWLER. 



widely separated by a strong morphological distinction, the 

 absence of dimorphism ; since the diflFerence between the 

 apical and lateral polyps in M. aspera is hardly strong enough 

 to be reckoned as such. That such a distinction should exist 

 between two species of a genus is very remarkable ; but^ con- 

 sidering the great antiquity of these forms, the similar struc- 

 ture of the colony in both, and the fact that they exhibit a 

 similar differentiation of certain mesenteries, it is not to be 

 inferred that their systematic relations are unsound. 



Note. 



For microscopic sections through both hard and soft parts 

 of the coral, such as are figured in (4) PL XLI, figs. 14, 15, I 

 have found the method, originally applied by v. 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 dis- 

 solved to make a block, rather larger when dry than the speci- 

 men. 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. 



