358 EVENINGS AT THE MICROSCOPE. 



that is at rest, a minute and momenta;-}" wave will be 

 seen to run rapidly along its length. All these circum- 

 Btances sliow that the ciliary motion is perfectly under 

 the control of the animal's will, not only in the aggre- 

 gate, but in every part. 



In an excellent memoir on this animal by Mr. R. 

 Patterson of Belfast,* there are some interesting ob- 

 servations on the power of its tissues to become tinged 

 with extraneous colours, a fact which may be useful to 

 you in your researches, as enabling you with more ease 

 and precision to demonstrate the internal structure. 



" From the inconsiderable quantity of solid ma- 

 terial," remarks this observer, " which enters into the 

 body of the Beroes, and the rapid circulation of water, 

 which is apparent throughout their frame, we would 

 natnrally suppose that any tinge which the body might 

 accidentally acquire would be extremely fugitive. It 

 was found, however, to be much less so than a priori 

 would have been expected. My attention was drawn 

 to this peculiarity by the circumstance of all my glass 

 vessels being one evening occnpied by Beroes and 

 Crusacea, so as to compel me to place a small Medusa 

 in a tin vessel, which chanced to be rusted at the seams. 

 Next morning the colourless appearance of the animal 

 was changed into a bright yellow, which appeared to 

 pervade every part, and doubtless arose from the oxide 

 of iron, diffused through the sea-water. This tint re- 

 mained during the entire day, although the animal was 

 transferred to pure sea-water. Wishing to try if the 

 vessels of the Beroe would become distinct, if filled 

 with some coloured fluid from which the animal could 

 Euddenly be withdrawn, and viewed through the usual 

 • Trans. Roy. Irish Academy, vol. six. pt. 1. 



