JELLY-FISHES. 311 



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 con- 

 trol of the animal's will, not only in the aggregate, but 

 in every part. 



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

 Patterson, of Belfast,* there are some interesting obser- 

 vations 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 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 

 suppose 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 

 appearance of the animal was changed into a bright 

 yellow, which appeared to pervade every part, and doubt- 

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



