INFUSORIAL ANIMALCULES. 139 



rows; and each revolves around its bulb, giving a singular appearance, 

 seeming to move together like a wheel upon its axle, whence their 

 name Rotifera ; in some of these muscles may be traced. The cilia 

 must not be mistaken by young microscopists for the stiff hairs and 

 bristles found on some animalcules, serving the purpose of locomotion 

 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 membrane 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 provided with a locomotive apparatus 

 of the same description, and has frequently been mistaken for such. 

 The animals more commonly employed for the examination of the cilia 

 are the oyster and the mussel j 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, and 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 producing 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 above 

 given ; the movements then will have become sluggish. If a power of 

 400 diameters be used, and that part of the cilia attached to the epi- 

 thelium scale carefully watched, each one will be found to revolve a 

 quarter of a circle, whereby a " feathering movement" is effected, and a 

 current in one direction constantly produced. In the higher animals 

 the action of the cilia can only be observed a short time after death. 

 In a polypus of the nose, when situated at the upper and back part of 

 the Schneiderian membrane, the cilia may be beautifully seen in rapid 

 action some few hours after its removal ; but in the respiratory and 

 other tracts, where ciliated epithelium is found, it would be almost im- 

 possible ever to see it in action, unless the body were opened imme- 



