432 



CILIARY MOTION. 



20 9. 



be perfectly involuntary, for they not only take place long after death, 



but even in detached portions, the ciliary cell being uninjured and entire. 



The seats of ciliary action are always moistened surfaces. The condi- 



tion for the continuance of the motion after death is accordingly that the 



surface shall be kept moist, but it is also necessary that a certain tem- 



perature should be observed, which in warm-blooded animals must not 



fall below 42 F. Even after the motion has completely ceased, a solu- 



tion of carbonate of potash re-excites it, but this does not take place 'with 



ammonia, because it injures the ciliated cells. 



Ciliary motion is independent of nervous agency. The control of tem- 



perature and of chemical reagents over it shows that it is of a physical 



nature. 



In the lower orders of life ciliary movement is relied on both for the 



Uses of ciliary purposes of locomotion and prehension. 



motion. " pig % 209 illustrates this in the case of 



a vorticella, the upper edge of which shows such a 



mechanism. It is often stated that in the higher an- 



imals the object is to determine a movement of the 



liquid which moistens the ciliated cells in the direc- 



tion of the outlet of the tube, or other surface which 



they line. In this way the action of the cilia may 



tend to the expulsion of material from the air-cells 



of the lungs into the bronchial tubes. In reptiles, 



whose urinary tubelets are furnished with this mech- ciliated animalcule. 



anism, the secretion may be urged thereby in the proper direction. 

 The contractile tissue which enables such animals as the hydra (Fig. 



Embryonic ^^) to execute movements of prehension and locomotion 



contractile tis- may perhaps be regarded as the rudimentary state of the 

 structures next to be described. The annexed sketch, from 



Trembley, illustrates the 

 manner of progression of 

 this animal. No trace of 

 a proper muscular fibre, 

 and none of a nervous 

 Hydra walking. system, have hitherto been 



detected in it. 



Of Muscular Motion. 



The muscular system consists of muscular fibres, tendons, bones, to- 

 gether with various accessory parts, such as ligaments, sheaths, bursa3 

 mucosiE, synovial capsules, fascia. Its action depends on the primary 

 fact that, under appropriate influences, muscular fibre shortens. 



Each voluntary muscle consists of a collection of fasciculi, which ex- 



