S8o 



MOTION. 



however, it is a special manifestation of a similar pro- 

 perty to that by which the other motions of animals are 

 effected, namely, by what we term vital contractility. The 

 fact of the more evident movements of the larger animals 

 being effected by a structure apparently different from 

 that of cilia, is no argument against such a supposition. 

 For, if we consider the matter, it will be plain that our 

 prejudices against admitting a relationship to exist between 

 the two structures, muscles and cilia, rests on no definite 

 ground ; and for the simple reason, that we know so little 

 of the manner of production of movement in either case. 

 The mere difference of structure is not an argument in 

 point ; neither is the presence or absence of nerves. The 

 movements of both muscles and cilia are manifestations of 

 force, by certain special structures, which we call respec- 

 tively muscles and cilia. We know nothing more about 

 the means by which the manifestation is effected by one of 

 these structures than by the other ; and the mere fact that 

 one has nerves and the other has not, is no more argument 

 against cilia having what we call a vital power of contrac- 

 tion, than the presence or absence of stripes from voluntary 

 or involuntaiy muscles respectively, is an argument for 

 or against the contraction of one of them being vital and 

 the other not so. Inasmuch then as cilia are found in 

 living structures only, and inasmuch as they are a means 

 whereby force is transformed (see Chap. II.), their peculiar 

 properties have as much right to be invested with the 

 term vital as have those of muscular fibres. The term 

 may be in both instances a bad one, it certainly is an 

 unsatisfactory one, but it is as good for one case as the 

 other. 



MUSCULAR MOTION. 



There are two chief kinds of muscular tissue, the striped \ 

 and the plain or unstriped, and they are distinguished by 

 structural peculiarities and mode of action. The striped 

 form of muscular fibre is sometimes called voluntary muscle. 



