xiv PROOFS OF ORGANISING MIND 291 



instrument which the organism has built up, and which then 

 ceases to form an integral portion of it — is, in fact, dead matter. 

 Hence, in no part of the fully grown feather is there any 

 blood circulation or muscular attachment, except as regards 

 the base, which is firmly held by the muscles and tendons 

 of the rudimentary hand (fore -limb) of the bird. This 

 beautiful and delicate structure is therefore subject to wear 

 and tear and to accidental injury, but probably more than 

 anything else by the continuous attrition during flight of 

 dust-laden air, which, by wearing away the more delicate 

 parts of the barbules, renders them less able to fulfil the 

 various purposes of flight, of body-clothing, and of conceal- 

 ment ; as well as the preservation of all those colours and 

 markings which are especially characteristic of each species, 

 and generally of each sex separately, and which, having all 

 been developed under the law of utility, are often as import- 

 ant as structural characters. Provision is therefore made 

 for the annual renewal of every feather by the process called 

 moulting. The important wing-feathers, on which the very 

 existence of most birds depends, are discarded successively 

 in pairs at such intervals as to allow the new growth to be 

 well advanced before the next pair are thrown off, so that 

 the bird never loses its power of flight, though this may be 

 somewhat impaired during the process. The rest of the 

 plumage is replaced somewhat more rapidly. 



This regrowth every year of so complex and important 

 a part of a bird's structure, always reproducing in every 

 feather the size and shape characteristic of the species, 

 while each of the often very diverse feathers grows in its 

 right place, and reproduces the various tints and colours on 

 certain parts of every feather which go to make up the 

 characteristic colours, markings, or ornamental plumes of 

 each species of bird, presents us with the most remarkable 

 cases of heredity, and of ever-present accurately directed 

 growth-power, to be found in the whole range of organic 

 nature. 



The Nature of Growth 



The growth of every species of organism into a highly 

 complex form, closely resembling one or other of its parents, 



