THE BEGINNINGS OF LIFE, 609 



themselves by the establishment of a moving equili- 

 brium, just as the internal tendencies of crystallizable 

 matter are satisfied (though here to a much greater 

 extent) as soon as it has assumed its appropriate 

 crystalline form. When a certain complexity of struc- 

 ture has been attained, it may be that things are much 

 as they have been represented to be by Mr. Darwin, 

 Mr. Herbert Spencer, and others. Many organisms 

 may not be prone to vary, unless under the influence 

 of ^spontaneously" induced, quasi-accidental changes 

 within their own economy, or unless subjected to the 

 disturbing influence of new conditions, or to the more 

 powerful and certain action of Natural Selection, aided 

 by ' use and disuse ' and other agencies. 



Multitudes of facts bearing upon the apparent per- 

 sistence, without variation, of particular species through 

 comparatively long periods, ought to impress us with 

 the possibility of the existence of such a limitation 

 to the internal proclivities towards higher organi- 

 zation which simpler living things display. Some of 

 these facts are alluded to by Mr. Darwin when he 

 says^ : — ^ It has been argued that, as none of the animals 

 and plants of Egypt of which we know anything have 

 changed during the last 3000 years, so probably none 

 have been modified in any other part of the world. The 

 many animals which have remained unchanged since 

 the commencement of the glacial period would have 

 been an incomparably stronger case, for these have 



^ ' Origin of Species,' 5th ed., p. 148. 

 VOL. II. R r 



