An easy way to observe this phenomenon is to detach, by scraping with a knife, a small piece of E. from the back of the throat of a living frog. The scales, moistened with water or serum,' will continue to exhibit the movement of their adherent cilia for a very considerable time, provided the piece be kept duly moistened. On one occasion. a piece prepared in this way by Mr. Bowman and Dr. exhibited motion for 17 hours; and it would probably have continued doing so for a longer time, had not the moisture around it evaporated; and if the E. is not removed from the body of an animal that had been killed, the motion continues much longer. In a turtle, after death by decapitation, it lasted, in the mouth, 9 days; in the trachea and lungs, 13 days; and in the esophagus, 16 days. In man and mammals, it seldom lasts 2 days, and usually ceases much sooner. The necessary condition for their movement appears to be the integrity of the cells to which they are attached; for as soon as these shrink up for want of moisture, or undergo any physical change, the cilia cease their characteristic action We know nothing with certainty regarding the mechanism or source of ciliary motion, except that (as it continues on detached E.) it is independent of both the vascular and ner vous systems.
This phenomenon exists very widely throughout the animal kingdom. Dr. Sharpey, in his article CILIA*' (published upwards of 40 years ago), notices its occurrence in the infusoria, In polyps and their ova, in acalephm, actinim, echinodermata, annelida, mol lusca, and the molluscoids (e.g., ascidians), in reptiles, birds, and mammals. Since the date of that article, it has been discovered in sponges, and in one or two cases in fishes; but it has never been found in any part of the body of articulate (crusta ceans, insects, or arachnidans). The parts on which it occurs are (1) the skin or sur face of the body, (2) the respiratory, (3) the alimentary, and (4) the genito-urinary terns; and it has been observed in the ova of numerous classes of animals, from reptlies downwards to infusoria. In most of the parts in which we observe it, its use appears to be of a mechanical nature—viz., to convey the fluids or other matters along the sur
faces on which the cilia exist, or, as in the infusoria, to carry the entire animal through the water.
1. Cilia have been found on the external surface in batrachian larva;, in molluscs, annelids, echinodermata, actinim, medusm, polypi, and infusoria. In most cases, their function is respiratory, but in many instance, t is also locomotive or prehensile.
2. Ciliary motion has been observed on the lining membrane of the air-passages of mammals, birds, and reptiles, where, whatever may be its other uses, it serves to convey the secretions along the membranes, together with any foreign matters that may be. present. It exists also on the external gills of batrachian larvae, and on the respiratory organs of mollusca and annelida. The cilia which exist externally on still lower animals without separate respiratory organs, assist in the respiratory process, by renewing the water on the surface.
3. It occurs in the mouth, throat, and gullet of various reptiles, and the alimentary canal of the mollusca, echinodermata, many annelida, and acalephia. It is not easy, as Dr. Sharpey observes, to see the purpose of the motion in all these cases. In some, it may merely convey secreted matters along the surface of the lining membrane; and in others it seems to serve in place of ordinary deglutition, to carry food into the stomach.
4. It is observed on the surface of the reproductive organs of mammals, birds, and reptiles. From the direction of the current being from without inwards, the office of the cilia may he to hurry down the ovum, in addition to removing the mucous secretion of the membrane.
In reptiles and fishes, ciliary motion exists at the neck of each uriniferous tube. The movement is directed towards the tube, and favors the flow of the watery portion of the secretion towards it.
There are some situations, both in man and the lower animals, in which it is difficult to determine what functions the ciliary motion can perform, as, for example, in man, in the ventricles of the brain; and in the frog, in the closed cavities of the pericardium and peritoneum.