ORGANIC EVOLUTION— THE FACTORS 67 



livingr organisms, is the same as that which causes, 

 under fit conditions, the growth of crystals. Under fit 

 conditions a crystal grows into a definite shape, accord- 

 ing to its kind, and so does an organism ; hut there the 

 analogy ends. Mr. Spencer, with more reason, might 

 have compared an organism to a river, and reasoned 

 from that basis. A river grows like a crystal and an 

 organism, but, like an organism and unlike a crystal, 

 waxes and wanes according to circumstances, is some- 

 what heterogeneous in composition, consists from time 

 to time of new material, and so forth. 



A crystal is essentially stable and homogeneous 

 throughout, and if in a solution there are molecules of 

 different kinds capable of crystallization, they crystallize 

 separately into different kinds of crystals. " Our very 

 definition of crystal structure is an arrangement of 

 particles, the same about one point as about every 

 other point ; hence, in one sense, the smallest fragment 

 of a crystal is complete in itself." ^ 



An organism is essentially unstable and heterogeneous; 

 the lowest organisms we are able to examine show in 

 their granular appearance unmistakable evidence of 

 heterogeneity ; higher organisms are obviously hetero- 

 geneous, and, according to Mr. Spencer, the physiological 

 visits in them must, if they have any existence, be 

 highly heterogeneous, since he speaks of the " specialized 

 molecules of each organ " (Pnndples of Biology, vol. i. 

 p. 178), though here he does not explain by what 

 process of crystallization the molecules of a crystal aie 

 "specialized"; since he speaks of "countless different 

 combinations of units derived from parents, and through 

 them from ancestors immediate and remote " (p. 268) ; 

 and since he speaks of " the mixed physiological units 

 composing any organism, being, as we have seen (?), 



' Elements of Oiystallography, p. 10. Williams ; Macmillaii and 

 Co., 1890. 



