CHAPTER III THE RATE OF GROWTH

any part became visible.*〝 After pointing out with his habitual care various exceptions, Darwin proceeds to lay down two general principles, viz. 〜that slight variations generally appear at a not very early period of life,〝 and secondly, that 〜at whatever age a variation first appears in the parent, it tends to reappear at a corôÙreôÙsponôÙding age in the offspring.〝 He then argues that it is with nature as with the fancier, who does not care what his pigeons look like in the embryo, so long as the full-grown bird possesses the desired qualities; and that the process of selection takes place when the birds or other animals are nearly grown up,〔at least on the part of the breeder, and presumably in nature as a general rule. The illustration of these principles is set forth as follows; 〜Let us take a group of birds, descended from some ancient form and modified through natural selection for different habits. Then, from the many successive variations having supervened in the several species at a not very early age, and having been inherited at a corôÙreôÙsponôÙding age, the young will still resemble each other much more closely than do the adults,〔just as we have seen with the breeds of the pigeon《....《Whatever influence long-continued use or disuse may have had in modifying the limbs or other parts of any species, this will chiefly or solely have affected it when nearly mature, when it was compelled to use its full powers to gain its own living; and the effects thus produced will have been transmitted to the offspring at a corôÙreôÙsponôÙding nearly mature age. Thus the young will not be modified, or will be modified only in a slight degree, through the effects of the increased use or disuse of parts.〝 This whole argument is remarkable, in more ways than we need try to deal with here; but it is especially remarkable that Darwin should begin by casting doubt upon the broad fact that a 〜difference in structure between the embryo and the adult〝 is 〜in some