RELATIVE STABILITY OF LIVING MATTER 



307 



its functionless teeth reduced to the primitive conical form, yet 

 often accompanied by rudimentary successionals 1 ; the splint 

 bones of horses, silent witnesses of what has befallen their neigh- 

 bor digits, and stern prophets of their own extinction ; the rudi- 

 mentary muscles of the scalp and the ears in man, these and 

 numberless similar vestiges of the past remind the student of the 

 tenacity with which vital activities persist when once established, 

 producing a rudimentary leg or wing, or lesser part, for indefi- 

 nite generations after its usefulness has ceased and all selection 

 has disappeared. 



SECTION V EVIDENCE FROM THE DIRECT ACTION 

 OF THE ENVIRONMENT 



All the evidence goes to show that the conditions of life exert 

 a direct and powerful action upon the extent of development 

 and the nature of the functions of living matter. We have only 

 to recall the characteristic reactions of certain chemical sub- 

 stances upon protoplasm, the influence of light, gravity, and 

 temperature, and the effect of even so slight a circumstance as 

 contact, to realize that living matter is exceedingly dependent 

 upon its environment. If we should forget for the moment that 

 racial lines are preserved distinct in spite of the environment, 

 we might readily come to believe with the Lamarckians that the 

 conditions of life are the supreme factors in directing evolution 

 and in fixing the type. 



To enter fully into the discussion of this phase of the question 

 at this point would be to repeat what has been said as to exter- 

 nal causes of variation, or to extend the examples cited, and 

 space can be afforded for neither. The student's attention is 

 invited to this phase of the question, however, for he should 

 acquire a just and reasonable conception of the relative stability 

 of living matter as shown by the abundance of the class of evi- 

 dence here hinted at rather than fully exploited. 



1 The fact that successional teeth are formed in a rudimentary state argues for 

 the fact that the teeth present are the first or milk teeth, which, being functionless, 

 are not discharged and replaced as in mammals generally, but, on the contrary, 

 persist through life. 



