THE MICROSCOPE. 147 



there must be a considerable amount of earthy impregnation, or they 

 would not be so brittle. How far, however, the treatment with 

 Caustic Potash they have probably undergone is answerable for 

 their present condition, I cannot say. Caustic Potash is a dan- 

 gerous ally, of which members will do well to be as careful as 

 they would of fire ; simple maceration, and then mounting as an 

 opaque object in a cell sufficiently deep to prevent all chance of 

 crushing, would be the best way to learn the true structure and 

 condition of these parts. 



Spines of Solaster Papposa (PI. 13, upper half). — The jointing 

 of the bony framework is very interesting ; and I wish particularly to 

 call the attention of those who are fortunate enough to reside at 

 the seaside, or who possess, or have access to. Marine Aquaria, to 

 the rounded openings in the integuments. They appear to be too 

 numerous and too regular to be accidental. "What is their pur- 

 pose ? Are they contractile ? Have they anything to do with a 

 circulation of the water to the body cavity ? Are they found in 

 others of the Echinodei-mata^ and if so under what modifications ? 

 The spines are arranged in bundles on short stalks ; the number 

 in different bundles varies considerably, and judging from their 

 arrangement as seen here, they must have a power of independent 

 motion — possibly like the vibracula in Polyzoa — for sweeping the 

 surface of the animal clear of extraneous particles. It will be 

 interesting to compare the spines of other species of Echinodcrmata 

 with those now under discussion, which appear to be really com- 

 pound spines, and sessile. 



Flustra foliacea (PI. 14) is a capital illustration of a typical 

 Polyzoon. Sometimes the marginal spines are quite absent; 

 at other times (as in a specimen now before me, gathered 

 on the coast at Boulogne), they are exceedingly numerous, there 

 being an additional one at either side, and one projecting like a 

 horn from the convex end of each cell. Such a condition is 

 probably owing to luxuriant growth under favourable circum- 

 stances. The horse-shoe-like plate at the opening of the mouth 

 serves the purpose of a little door, opening and shutting at will. 

 An ovicell is represented in Figs, i and 3 ; specimens are 

 occasionally found thickly covered with these curious egg-capsules, 

 of which an interesting description has been given by the Rev. 

 Thomas Hincks in the " Poi)ular Science Review." I have seen, 

 after storms, pieces of this Flustra thrown up with the tenants of 

 these elegant little "berceaunettes" in full vigour of life, and expand- 

 ing beautifully when put into a basin of sea-water. It is well worth 

 while to try and give permanence to such a display. This has 

 been successfully accomplished in many cases by dropping gin 



