yS BIOLOGICAL LECTURES. 



determine its figure at every instant of its existence. There 

 may be those, however, who will find fault with my identifi- 

 cation of the motions of an amoeboid with that of a whirl- or 

 vortex-ring of particles. It may be well, also, to explain here 

 that this notion has nothing to do with the physical con- 

 ception of Lord Kelvin respecting the existence of vortex 

 atoms. The identification of amoeboid motion with a vortex- 

 ring of particles is perfect, provided certain reservations are 

 made that grow out of the very nature of the conditions and 

 nature of amoeboid motion. In a typical smoke- or vortex- 

 ring the impulse of rotation that impels all its particles is 

 imparted from without; in the living vortex-ring secular 

 changes in the nature of its constituent particles condition 

 its motions and provoke them. And, while it is true that the 

 energy that drives the living vortex-ring is primarily derived 

 from without, it is not set free until the constituent particles 

 have changed their dimensions, affinities, and reciprocal attrac- 

 tions within the ring, due to causes acting antecedently from 

 without. The living vortex-ring is a constantly changing, 

 closed, and regenerative dynamical system; the other is a 

 dynamical system that derives all its energy from without in 

 the form of a single impulse, and comes to rest after a time, 

 owing to the friction of its superficial particles with their 

 surroundings. 



It may be objected, also, that there is only a remote resem- 

 blance of a smoke-ring to that of the flux of living particles 

 through an amoeboid organism. This objection may be met 

 by the statement, that not only do I suppose the li\-ing vortex- 

 ring to be flattened by its gravity, but I also suppose it to 

 have no central opening, and that the median longitudinal 

 stream of particles represents the ])oint where the opening 

 would be in a smoke-ring — now a line in Amoeba — along 

 which the central "living" vortex current is flowing. I 

 moreover suppose that the ring is greatly elongated, owing 

 to the viscosity of its substance and the adhesion of the 

 surface of the living amoeboid to the substratum upon which 

 it moves. I would not have any one suppose that I imagined 

 that amoeboids ever existed that had a central opening in them 



