CILIARY MOVEMENT. 
57 
corn when depressed "by the wind; and if a number be 
affected in succession with this motion, the appearance of 
progressive waves following one another is produced, as when 
a corn-field is agitated by repeated gusts. When the ciliary 
motion is taking place in full activity, however, nothing can 
be distinguished save the whirl of particles in the surround¬ 
ing liquid; and it is only when the rate of movement 
slackens, that the shape and size of the individual filaments, * 
and the manner in which their stroke is made, can be made 
out. The motion of the cilia is not only quite independent 
(in all the higher animals at least) of the will of the animal, 
but is also independent even of the life of the rest of the 
body; being seen to continue after the death of the animal, 
and even going on with perfect regularity in parts separated 
from the body. Thus, isolated epithelium-cells have been 
seen to swim about actively in water, by the agency of their 
cilia, for some hours after their detachment from the mucous 
membrane of the nose; and the regular movement of cilia 
has been noticed fifteen days after death, in the body of a 
tortoise in which putrefaction was already far advanced. In 
the gills of the Eiver Mussel, which are amongst the best 
objects for the study of this most curious phenomenon, the 
movement endures with similar pertinacity.—The purpose of 
this remarkable agency is obviously to propel fluids over the 
surfaces which are furnished with cilia. We find it taking 
the most important share in the functions of life among the 
lowest classes of animals. Thus, in Animalcules of various 
kinds, the cilia are the sole instruments, not merely for the 
production of those currents in the water which may bring 
them the requisite supplies of air and food, but also for pro¬ 
pelling their own bodies through the liquid. In most 
Zoophytes, and in the inferior Mollusks, which pass their 
lives with little or no change from one spot to another, the 
motion of the cilia lining the alimentary canal and clothing 
the gills (where such have a special existence), draws into the 
mouth the minute currents which serve as food, and also 
renews the layer of water in contact with the respiratory 
surface. The gills of Fishes are not furnished with cilia, 
another provision being ^made by muscular action for conti¬ 
nually driving fresh streams of water over them; but the 
motion may be very well seen upon the gills of the young 
