MOVEMENTS OF MAN AND ANIMALS. 151 



along, in fixed directions, round the interior of the cells, passing, when these 

 are oblong, up one side and down the other, in regular and continued order 

 the movement really occurring in the fluid contents of the cells, and the solid 

 particles being thus carried along. It has been supposed that the cells were 

 provided with cilia on their internal surface ; but of this there is no proof. It 

 would rather seem that the internal surface of the periplast or cell-wall is lined 

 with a layer of contractile protoplasm, in which progressive undulatory move- 

 ments take place ; but how these are caused or regulated is unknown. It is 

 interesting to find in these various vegetable movements, if not an identity 

 with, at least a simulation of, the lowest forms of animal contractility and 

 movements. 



MOVEMENTS OF MAN AND ANIMALS. 



The various kinds of motion which we have now considered, whether 

 muscular, ciliary, sarcodous, or protoplasmic, are employed, as we 

 shall hereafter see, both in man and animals, not only in the functions 

 of animal life, as in motion and sensation, but also in those of vegeta- 

 tive life, as, for example, in the actions of the digestive apparatus, of 

 the organs of circulation, and those of nutrition, secretion, excretion, 

 respiration, and reproduction. The movements of animal life, properly 

 so called, which have now to be considered, have for their immediate 

 purpose either the performance of the various acts of locomotion, pre- 

 hension^ or manipulation, or they may aid in the exercise of the organs 

 of the senses, or they may be called into play in expression, or in the 

 production of voice and speech. In reference to these intrinsic move- 

 ments, the animal body may be regarded as a machine, differing from 

 ordinary machines, in being endowed with life, in possessing within 

 itself a source of action or power, viz., vital contractility, and in being 

 composed of certain mechanical parts destined to be moved on each 

 other, except in the lowest forms of animals, in subjection to the inter- 

 nal control of the nervous system, so as to yield intrinsically regulated 

 mechanical effects. 



Thus, in locomotion, the body, entirely, or by its parts, acts on some 

 external medium, whether solid, fluid, or aerial; and, in consequence 

 of the resistance or reaction of that medium, is moved through space. 

 In prehension, and its higher form, manipulation, certain parts of the 

 body seize, act upon, and utilize materials external to it, according to 

 the innumerable dictates of want, desire, or reasonable will. In aiding 

 the sensory organs, movements are impressed either upon the head, or 

 upon the various sensory organs, or their parts and appendages. In 

 expression, all parts of the body may be set in motion, but in the 

 higher animals, and in man, particularly, the features. In the pro- 

 duction of voice, peculiar and rhythmical vibrations of a speciaj part 

 of the frame of air-breathing animals, accompanied by synchronous 

 vibrations in the air, are generated by movements set up in the respira- 

 tory apparatus. Finally, speech, which is peculiar to man, and re- 

 sults from the modification of vocal or whispered sounds, is due like- 

 wise to muscular actions which are accomplished by the throat, mouth, 

 and lips. 



