DYNAMICS IN EVOLUTION. 79 



like a smoke-ring. I have only used this comparison because 

 of the obvious identity of the living and dead vortices, when 

 proper allowance is made for the physical conditions under 

 which both subsist on account of the different nature of their 

 constituent substances. The outer molecular shell, for example, 

 of a living vortex-ring is fixed to its substratum, and is only 

 involuted " posteriorly," and evoluted "anteriorly" as it moves 

 over a fixed surface. These ideas once clearly grasped, will 

 enable any one to see that, underlying the apparent unlikeness 

 of the smoke-ring to a living amoeboid vortex, there is in reality 

 a fundamental similarity. The kind of "contractility" which is 

 exhibited by an amoeboid is thus also seen to be fundamentally 

 different in nature from that presented by a muscle, in which 

 contraction is conditioned by a vastly more complex structure. 

 When an Amoeba passes into the resting stage its plasma is 

 very apt to assume an almost perfectly globular form. Its 

 pseudopodia are retracted ; its surface becomes smooth, and 

 the whole organism passes into the almost homogeneous, 

 quiescent or lethargic condition of a ball of protoplasm that no 

 longer manifests its characteristic types of motion and irrita- 

 bility, at least externally. JUnequal surface-tensional disturb- 

 ances no longer affect it ; it is now under the domination of 

 the same physical influences that determine the globular form 

 of a sphere of oil in a mixture of alcohol and water of the same 

 specific gravity as itself. Its cytoplasmic substance is nearly 

 or quite homogeneous, and the excessively slow and torpid meta- 

 bolic processes, within the protoplasmic mass of the Amoeba, 

 now secrete or pour out a cuticle or envelope over its surface 

 and in which the organism is said to be "encysted." All of 

 these processes are purely dynamical, just as were all of those 

 associated with the motion of the organism. Not only are all 

 of these processes dynamical, but all are also directly "adap- 

 tive," in virtue of the fact that the equilibria successively 

 attained are merely a quantitative dynamical response from 

 within a " living " molecular mechanism to a change in external 

 energy-conditions. All " adaptation " is to be so interpreted, 

 so that "natural selection" may be at last resolved into pure 

 energy-factors, and thus brought into coordination with the 



