JELLY-FISHES. 311 



paddles are set in a fixed line of curvature instead of a 

 revolving circle. The effect, however, is exactly the same : 

 that of paddling the beautiful little globe vigorously through 

 the water. The prismatic colours are produced by the 

 play of light on their glittering surfaces, which are ever 

 presented to the eye of the beholder at changing angles. 



We rarely see these rows of paddle-fins wholly at rest, 

 but occasionally one or two bands will be alone in a state 

 of vibration ; or one or more will suspend their action 

 while the rest are paddling. Sometimes in a band that is 

 at rest, a minute and momentary wave will be seen to run 

 rapidly along its length. All these circumstances show 

 that the ciliary motion is perfectly under the control of 

 the animal's will, not only in the aggregate, but in every 

 part. 



In an excellent memoir on this animal by Mr. E. Patter- 

 son, of Belfast,* there are some interesting observations 

 on the power of its tissues to become tinged with extra- 

 neous 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 material" 

 (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 naturally sup- 

 pose that any tinge which the body might accidentally 

 acquire would be extremely fugitive. It was found, how- 

 ever, 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 

 occupied by Beroes and Crustacea, 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 appear- 

 ance of the animal was changed into a bright yellow, which 

 appeared to pervade every part, and doubtless arose from 

 * " Trans. Boy. Irish Academy," vol. xix. pt. 1. 



