THE FACTORS OF ORGANIC EVOLUTION. 771 



If it be asked bow it happens that there have been recorded multi- 

 tudinous instances of variations fortuitously arising and reappearing 

 in offspring, while there have not been recorded instances of the trans- 

 mission of changes functionally produced, there are three replies. The 

 first is that changes of the one class are many of them conspicuous, 

 while those of the other class are nearly all inconspicuous. If a child 

 is born with six fingers, the anomaly is not simply obvious but so 

 startling as to attract much notice ; and if this child, growing up, has 

 six-fingered descendants, everybody in the locality hears of it. A 

 pigeon with specially-colored feathers, or one distinguished by a broad- 

 ened and upraised tail, or by a protuberance of the neck, draws atten- 

 tion by its oddness ; and if in its young the trait is repeated, occa- 

 sionally with increase, the fact is remarked, and there follows the 

 thought of establishing the peculiarity by selection. A lamb disabled 

 from leaping by the shortness of its legs, could not fail to be observed ; 

 and the fact that its offspring were similarly short-legged, and had a 

 consequent inability to get over fences, would inevitably become 

 widely known. Similarly with plants. That this flower had an extra 

 number of petals, that that was unusually symmetrical, and that an- 

 other differed considerably in color from the average of its kind, would 

 be easily seen by an observant gardener ; and the suspicion that such 

 anomalies are inheritable having arisen, experiments leading to fur- 

 ther proofs that they are so, would frequently be made. But it is not 

 thus with functionally-produced modifications. The seats of these are 

 in nearly all cases the muscular, osseous, and nervous systems, and the 

 viscera — parts which are either entirely hidden or greatly obscured. 

 Modification in a nervous centre is inaccessible to vision ; bones may 

 be considerably altered in size or shape without attention being drawn 

 to them ; and, covered with thick coats as are most of the animals 

 open to continuous observation, the increases or decreases in muscles 

 must be great before they become externally perceptible. 



A further important difference between the two inquiries is that 

 to ascertain whether a fortuitous variation is inheritable, needs merely 

 a little attention to the selection of individuals and the observation of 

 offspring ; while to ascertain whether there is inheritance of a func- 

 tionally-produced modification, it is requisite to make arrangements 

 which demand the greater or smaller exercise of some part or parts ; 

 and it is diflicult in many cases to find such arrangements, troublesome 

 to maintain them even for one generation, and still more through suc- 

 cessive generations. 



Nor is this all. There exist stimuli to inquiry in the one case 

 which do not exist in the other. The money-interest and the interest 

 of the fancier, acting now separately and now together, have prompt- 

 ed multitudinous individuals to make experiments which have brought 

 out clear evidence that fortuitous variations are inherited. The cat- 

 tle-breeders who profit by producing certain shapes and qualities ; the 



