26 TEE FACTORS OF ORGANIC EVOLUTION. 



much notice ; and if this child, growing up, has six- 

 fingered descendents, everybody in the locality hears of 

 it. A pigeon with specially-coloured feathers, or one 

 distinguished by a broadened and upraised tail, or by a 

 protuberance of the neck, draws attention by its oddness ; 

 and if in its young the trait is repeated, occasionally with 

 increase, the fact is remarked, and there follows the thought 

 of establishing the peculiarity by selection. A lamb dis 

 abled 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 another differed considerably in colour 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 further 

 proofs that they are so, would frequently be made. JBut it. 

 is not thus with functionally-produced modifications. Tho 

 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, tho 

 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 functionally- 

 produced modification, it is requisite to make arrangements 

 which demand the greater or smaller exercise of some part 



