CH. III.] CILIARY MOTION 29 



ticular group. The gills of many animals are covered with cilia; 

 and the cells of the kidney tubules in some animals are ciliated. 



Ciliary Motion. 



Ciliary motion reminds one of amoeboid movement, but it is much 

 more rapid, and more orderly. It consists of a rhythmical movement 

 of the cilia, a bending over, followed by a lessening of the curvature, 

 repeated with great frequency. 



When living ciliated epithelium, e.g., from the gill of a mussel, or 

 from the mouth of the frog, is examined under the microscope in a 

 drop of 075 per cent, solution of common salt (normal saline solution), 

 the cilia are seen to be in constant rapid motion, each cilium being 

 fixed at one end, and swinging or lashing to and fro. The general 

 impression given to the eye of the observer is very similar to that 

 produced by waves in a field of corn, or swiftly running and rippling 

 water, and the result of their movement is to produce a continuous 

 current in a definite direction, and this direction is the same on the 

 same surface, being usually in the case of a cavity towards the 

 external orifice. 



There is not only rhythmicality in the movement of a single 

 cilium, but each acts in harmony with its fellows in the same cell, 

 and on neighbouring cells. 



The uses of cilia can from the above be almost guessed ; in the 

 respiratory passages they create a current of mucus with entangled 

 dust towards the throat ; in the Fallopian tube or oviduct they assist 

 the ovum on its way to the uterus ; in the gullet of the frog they act 

 downwards and assist swallowing ; in the ciliated protozoa they are 

 locomotive organs. Over the gills of marine animals they keep up a 

 fresh supply of water, and in the case of the rotifers, which are fixed 

 animals, the current of water brings food to the mouth. 



Ciliary motion is independent of the will, and of the influence 

 of the nervous system. It may continue for several hours after 

 death or removal from the body, provided the portion of tissue under 

 examination be kept moist. Its independence of the nervous system 

 is shown also in its occurrence in the lowest invertebrate animals, 

 which are unprovided with anything analogous to a nervous system. 

 The vapour of ether or chloroform and carbon dioxide arrest the 

 motion, but it is renewed on the discontinuance of the application. 

 The movement ceases when the cilia are deprived of oxygen, although 

 it may continue for a time in the absence of free oxygen, but is 

 revived on the admission of this gas. The contact of various sub- 

 stances, e.g., bile, strong acids, and alkalis, will stop the motion 

 altogether ; but this depends on destruction of the delicate substance 

 of which the cilia are composed. Temperatures above 45 3 C. and near 



