FOURTH LECTURE. 



DYNAMICS IN EVOLUTION. 



JOHN A. RYDER. 



THE statement that energy, in its kinetic and static forms, 

 has been a factor in the production of the shapes of organisms, 

 does not admit of question at the present time. In order that 

 the data in support of this statement may be presented in their 

 simplest forms, it is necessary to begin with the consideration of 

 the physical causes of the configuration of some of the simplest 

 unicellular organisms. In this way it will eventually be pos- 

 sible to pass from the consideration of the unicellular to that 

 of the multicellular type, viewed from the same standpoint. 

 It requires but little familiarity with the principles of physical 

 science to discover that similar laws hold with respect to the 

 behavior of fluid and semi-fluid bodies, notwithstanding the 

 fact that we may have before us, in one case, a so-called 

 " dead " fluid body, and in the other, a fluid or fluent " living " 

 chemical compound or mixture of compounds. Though the one 

 presents the phenomena of 'dead,' and the other of living, 

 matter, both exhibit the similar and common properties of 

 fluids, namely, those of surface-tension, viscosity and adhesion 

 to the surfaces of other bodies, with which they are brought 

 into contact. Under certain conditions, also, the semi-fluid 

 cells of living bodies undergo reciprocal deformation or altera- 

 tion in configuration, as a result of the interaction of the 

 inherent forces above specified, in ways so precisely similar to 

 those seen when a number of semi-fluid, or fluid dead masses, 

 are juxtaposed or brought into contact, that the resemblances 

 are seen to be due to the cooperation of closely similar, if not 

 identical, forces and properties. 



