1. Summary of the animals in which the ciliary motion has been discovered.
From the foregoing facts it appears that the ciliary motion is a phenomenon which prevails most extensively in the animal kingdom, hav ing been found in the highest as well as the lowest members of the Zoological scale. Among Vertrebated Animals it has been dis covered in Mammalia, Birds, and Reptiles, viz. the Batrachia, Sauria, Ophidia, and Chelonia. Of the Invertebrata it has been found in Mollusca, viz. Gasteropoda, Conchi ferous acephala, and Tunicata ; in Annelida, viz. Aphrodita, Arenicola, and many Tubi colar worms, also in P/anarice and 1Vaiades; in Echinodermata, viz. the Asterias and Echinus; in Actiniw ; in Medusw; in Polypi; in Sponges; and in Infusoria. It is a remarkable fact that no trace of it has been observed in Fishes. I at one time supposed that the pendent filaments of the gills of the fcetal Skate and Shark might probably be found to exhibit it ; but my friend, Dr. Allen Thomson, has care fully inspected those of the Skate without being able to perceive any appearance of it.* 2. Organs or parts of the body in which the ciliary motion has been ascertained to exist.
These may be referred to four heads, viz. the skin or surface of the body, the respiratory, alimentary, and reproductive systems. Its use in all these cases, or the function in general of the cilia, is to convey fluids or other matters along the surface on which the cilia are placed, or, as in the Infusoria, to carry the entire animal through the fluid.
a. Surface of the body.—Cilia have been found on different parts of the external surface, in Batrachian larv, in Mollusca, Annelida, Echinodermata, Actiniw, Medusa!, Polypi, and Infusoria. Their function in this situation is various ; in most cases it is evidently respi ratory, but in many instances it is also locomo tive, as in Infusoria and Medusze, or prehensile, as in Infusoria and Polypi ; and perhaps it is in some animals subservient to the sense of touch or smelling, as may be conjectured with regard to the cilia on the tentactila of some Mollusca.
b. Respiratory system.—The ciliary motion has been observed on the lining membrane of the air-passages of Mammalia, Birds, and Rep tiles; and there, whatever may be its other uses, it at least serves to convey the secretions along the membranes, together with foreign matters, if any are present. It exists also on
the external gills of Batrachian larva2, and on the gills of Mollusca and Annelida. In other Annelida, in Echinodermata and Actiniw, it is found on the external surface of the viscera and on the parietes of the cavity containing them, to vvhich cavity the water has access. The pores and canals of the Sponge are pro bably both respiratory and alimentary passages, and under this head we must refer again to the cilia on the external surface of Medusze, Polypi, and Infusoria, as belonging partly to the respi ratory system. The use of the ciliary motion on the respiratory organs of animals with aquatic respiration is obviously to renew the water on the respiring surface.
c. Alimentary system.—The motion occurs in the mouth, throat, and gullet of Reptiles, in the entire alimentary canal of Mollusca, on the intenial surface of the intestine and ccecal appendages of the Aphrodita, within the sto mach and cceca of the Asterias, in the stomach of the Actinia, in the canals of the Sponge, which no doubt belong partly to the alimentary system, and in the mouth, throat, stomach, and intestine of several Polypi. It is not easy to see the purpose of the motion in all these cases. ln some it may merely convey secreted matters along the surface of the lining mem brane; in Polypi it agitates the food within the alimentary cavity, and in several instances it seems almost to serve in place of ordinary deglutition, to carry food into the stomach.
d. Reproductive organs.—The phenomenon occurs on the mucous membrane cf the Fallo pian tubes, uterus, and vagina of Mammalia, and of the oviduct in Birds and Reptiles. From the direction, of the impulsion being from within outwards, it is difficult in the meantime to assign any other office to the cilia in this situation than that of conveying outwards the secretion of the membrane, unless we suppose that it also brings down the ovum.