MOVEMENT 



of the single cell; but in the histona, the multicellular 

 tissue-forming organisms, they are the outcome of the 

 combined movements of the many cells which compose 

 the tissue. Careful anatomic study and experimental 

 physiological scrutiny of the motor processes are, there- 

 fore, first directed, in the case of the histona, to clearing 

 up the nature and activity of the special cells which com- 

 pose the tissue, and then the structure and functions of 

 the tissue itself. When we start from this point, and 

 survey the manifold active motor phenomena of the 

 histona as a whole, we see at once an essential agree- 

 ment in the phoronomy of the two kingdoms of the 

 metaphyta and metazoa, in the sense that at the lower 

 stages the chemical and physical character of the motor 

 processes can be clearly shown and can be traced to an 

 interchange of energy in the plasm of the cells that make 

 up the tissue. In the higher stages, however, we find 

 striking differences, the voluntary character of many 

 autonomous movements being very conspicuous in the 

 higher animals, and thus the great problem of the free- 

 dom of the will is added to the purely physiological 

 questions of stimulated movement, growth-movement, 

 etc. 



Moreover, the movements of the metazoa are much 

 more varied and complicated than those of the metaph- 

 yta, in consequence of the higher differentiation of 

 their sense-organs and the centralization of their ner- 

 vous system. The former have generally free locomotion 

 and the latter not. The special mechanism of the or- 

 gans of movement is also very different in the two 

 groups. In most of the metazoa the chief motor organs 

 are the muscles, which have developed in the highest 

 degree the power of definitely directed contraction and 

 expansion. In most of the metaphyta, on the other 

 hand, the chief part of the movements depend on the 

 strain of the living plasm, or what is called the turgor 

 z8 273 



