TRANSLATOR'S PREFACE 



faculty of flight? Many of them are certainly unable to 

 fly when they are first hatched, and have to practise for some 

 little time, even when fully fledged, before they can sustain 

 themselves in the air for any length of time. If such birds 

 were never allowed to use their wings at all for several 

 generations, would they not gradually lose the faculty of 

 flight altogether ? The answer is given by our domestic 

 ducks and fowls which, although not altogether prevented 

 from using their wings, have almost lost the power of flight. 



But it may be urged that the wings of birds are 

 certainly inherited. Quite true ; and is Professor Weismann 

 in a position to assert that no structural modifications are 

 produced by constant pianoforte -playing during several 

 generations, or that such structural modifications are pro- 

 duced but not inherited ? I think it may be safely assumed 

 that neither he nor any one else knows what changes in 

 the muscles and nerves of the hands are produced by the 

 practice of pianoforte-playing: although it is certain that 

 extraordinary skill in the art is connected with peculiarities 

 in the condition of those muscles and nerves. 



Moreover, it can be shown by actual facts that all modi- 

 fications, all progressive development of a structural character, 

 are not due to " sexual mixture," that is, to the combination 

 of the hereditary characters of the parents. I possess a 

 female cat with six toes on every foot. One of the kittens 

 of this cat has six toes on each hind foot, five on the left fore 

 foot, and seven on the right fore foot. But the left foot is 

 not normal, the inner toe or pollex is as large as two of the 

 others. It is practically certain that the father of this 

 kitten was an ordinary cat with the usual number of toes, 

 and the abnormal number of toes on the right fore foot has 



