THE FACTORS OF ORGANIC EVOLUTION. 35 



lead protected and pampered lives. Of the numerous cases 

 named by Mr. Darwin, it is observable that they are 

 yielded not by one class of parts only, but by most if not 

 all classes by the dermal system, the muscular system, the 

 osseous system, the nervous system, the viscera ; and that 

 among parts liable to be functionally modified, the most 

 numerous observed cases of inheritance are furnished by 

 those which admit of preservation and easy comparison 

 the bones : these cases, moreover, being specially signifi 

 cant as showing how, in sundry unallied species, parallel 

 changes of structure have occurred along with parallel 

 changes of habit. 



What, then, shall we say of the general implication ? 

 Are we to stop short with the admission that inheritance 

 of functionally-produced modifications takes place only in 

 cases in which there is evidence of it ? May we properly 

 assume that these many instances of changes of structure 

 caused by changes of function, occurring in various tissues 

 and various organs, are merely special and exceptional 

 instances having no general significance ? Shall w T e 

 suppose that though the evidence which already exists 

 has come to light without aid from a body of inquirers, 

 there would be no great increase were due attention 

 devoted to the collection of evidence ? This is, I think, 

 not a reasonable supposition. To me the ensemble of the 

 facts suggests the belief, scarcely to be resisted, that the 

 . / inheritance of functionally-produced modifications takes 

 place [universally. Looking at physiological phenomena as 

 conforming to physical principles, it is difficult to conceive 

 that a changed play of organic forces which in many 

 cases of different kinds produces an inherited change of 

 atrnfitnrftj dnpa not fin f/hjs in all oases. The implication, 

 very strong I think, is that the action of every organ 

 produces on it a reaction which, usually not altering its 

 rate of nutrition, sometimes leaves it with diminished 

 nutrition consequent on diminished action, and at other 



