242 THE MICKOSCOPE. 



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 use- 

 ful substitutes for the more expensive and difficultly-managed cells. In 

 this manner specimens of the genera Cycloum, Membranipora, Alcyoni- 

 dium, and Crisia, 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 Laomedea3, Grantise, and their 

 allies; whilst the elegant Tubularise afford an ornament 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 inte- 

 resting results are produced. For this purpose, let a piece of selenite 

 be placed on the stage of the microscope, and the polarising prisms 

 arranged so that the ray transmitted is absorbed by the analyser. 



If a specimen of Sertularia operculuta, 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 distinctly 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 orange-yellowish colour. 



This zoophyte is often covered with minute bivalve shells, distin- 

 guished 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 beau- 

 tiful colours. 



Sertularia JUicula forms an interesting object ; the waved stem 

 becoming of a dusky-red, whilst the cells assume but little colour, ren- 

 ders their mutual relation very obvious. Sertularia abietina is also a 

 fine object, especially when loaded with vesicles, as it often is in the 

 autumn. Plumularia falcata acquires fresh beauty under polarised 

 light, the cells being a pale green, whilst the tubular stem becomes 

 of a crimson hue j thus presenting a feathered appearance. 



The most splendid tints are exhibited by the calcareous structure 



