296 THE MICROSCOPE. 



each revolves around its bulb, giving a singular appearance, 

 seeming to move together like a wheel upon its axle, 

 whence their name Rotifera ; in a few of these muscles can 

 be traced. The cilia must not be mistaken by the young 

 microscopist for the stiff hairs and bristles found on some, 

 and serving, as before stated, for the purpose of locomo- 

 tion in crawling or climbing. 



If the roof of the mouth of a living frog be scraped 

 with the end of a scalpel, and the detached mucous mem- 

 brane placed on a glass slide, and examined with a power 

 of 300 diameters, the ciliated epithelium-cells will be well 

 seen. When a number of these are collected together, the 

 movement is effected with apparent regularity; but in 

 detached scales it is often so violent, that the scale itself is 

 whirled about in a similar manner to an animalcule pro- 

 vided with a locomotive apparatus of the same description, 

 and has frequently been mistaken for such. The animals 

 commonly employed for the examination of the cilia are 

 the oyster and the mussel; but the latter are generally 

 preferred. 



To exhibit the movement to the best advantage, the 

 following method must be adopted : open carefully 

 the shells of one of those molluscs, spilling as little as 

 possible of the contained fluid; then with a pair of fine 

 scissors remove a portion of one of the gills (branchiae) ; 

 lay this on a slide, or the tablet of an animalcule cage, and 

 add to it a drop or two of the fluid from the shell ; by 

 means of the needle-points separate the filaments one from 

 the other, cover it lightly with a thin piece of glass, and 

 it is ready for examination. The cilia may then be seen 

 in several rows beating and lashing the water, and pro- 

 ducing an infinity of currents in it. If fresh water instead 

 of that from the shell be added, the movement will speedily 

 stop ; hence the necessity of the caution of preserving the 

 liquid contained in the shell. To observe the action of any 

 one of the cilia, and its form and structure, some hours 

 should be allowed to elapse after the preparation of the 

 filaments as above given, their movements then will have 

 become sluggish. If a power of 400 diameters be used, 

 and that part of the cilia attached to the epithelium scale 

 carefully watched, each one will be found to revolve a 



