PRESERVATION OF THE POLYP1DOMS OF ZOOPHYTES. 409 



place ; and many of the tentacles previously concealed will 

 emerge from their cells. After being left in vacuo for 

 a few hours, the bottles should be filled up, closely corked, 

 and tied over, like anatomical preparations in general. For 

 all examinations with a one or two-inch object-glass, these 

 bottles are most excellent, and afford cheap and useful 

 substitutes for the more expensive and difficultly- managed 

 cells. In this manner, specimens of the genera Membrani- 

 porce, Alcyonidce, and Crisiadce, &c., exhibit their structure 

 most beautifully. 



" A few dozen of these little bottles hardly occupy any 

 room, and would form a useful accompaniment to the 

 microscopist by the sea-side. Any one visiting the caverns in 

 St. Catherine's Island at Tenby, could reap a harvest which 

 would afford amusement and instruction for many weeks. 

 These caverns are so rich in zoophytes and sponges, that 

 they are literally roofed with the Laomedece, Grantice, and 

 their allies ; whilst the elegant Tubularice afford an orna- 

 ment to the shallow pools on the floor ; and the walls are 

 wreathed with the pink, yellow, green, and purple 

 Actiniae. 



" When these objects are examined by polarised light, 

 most interesting results are produced. For this purpose, 

 let a piece of selenite be placed on the stage of the micro- 

 scope, and the polarising prisms arranged so that the ray 

 transmitted is absorbed by the analyser. If a specimen of 

 Sertularia operculata be placed on the selenite stage, and 

 examined with a two-inch object-glass, the central stem is 

 shown to be a continuous tube, assuming a pink tint 

 throughout its whole extent. The cells appear violet in 

 colour; their pointed orifices are seen much more dis- 

 tinctly than when viewed with common light. The vesicles 

 are paler than the rest of the object ; and their lids, which 

 so remarkably resemble the operculum of the theca of a 

 moss, are beautifully distinct, being of an orange-yellowish 

 colour. This zoophyte is often covered with minute 

 bivalve shells, distinguished by the naked eye from the 

 vesicles only by their circular form; and these, when 

 present, add much to the beauty of the specimen, pre- 

 senting a striated structure, and becoming illuminated 

 with most beautiful colours. 



