312 A HISTORY OF BIRDS 



fied by use no one disputes. A wing increases or decreases 

 according to the amount of work exacted from it. But there is 

 no evidence that the effects, either one way or another, of the 

 use of this organ during the life of the individual, are trans- 

 mitted to its offspring. The vestigial wings of the Ostrich 

 tribe, the great Auk, and the Dodo are not evidence of the 

 inherited effects of disuse, but of the cessation of the action 

 of selection. So soon as flight became unnecessary for the 

 continuance of life, birds with wings below the average mean 

 stood as good a chance in the struggle for existence as those 

 wherein the wings were larger. But, we repeat, this degree 

 in largeness or smallness was congenital, and not transmitted 

 as a consequence of use or disuse. The struggle for life im- 

 poses a certain minimum standard of efficiency in more or 

 fewer characters. These characters are, or are not, inherent 

 in the germ plasm : and on this depends the survival of the 

 individual. The continuous elimination of birds with wings 

 below a certain standard keeps up the efficiency of flight. So 

 soon as this process of elimination ceases, the decay of the 

 wing commences, though the decline may be imperceptible in 

 any given generation. Physical characters acquired by the 

 individual during its life -time, like knowledge, die with the 

 individual by whom they were acquired. In a word, soraato- 

 genetic characters impressed on an individual during its life- 

 time are not transmissible to offspring. The only characters 

 which can be transmitted are blastogenetic — those inherent in 

 the germ plasm : and these have come into being through the 

 agency of natural selection, which has operated by adopting, 

 or rejecting, the permutations which are inevitable owing to 

 the instability of living matter. 



The following are some of the more striking of the instances 

 which have been put forward as evidence demonstrating the 

 truth of the doctrine of the transmissibility of " acquired 

 characters ". 



Perhaps the most interesting is that brought forward by 

 Dr. Hans Gadow, whose work as a morphologist gives added 

 weight to his arguments. 



Dr. Gadow has endeavoured to show that the very remark- 

 able shoulder girdle and alimentary canal of that very remark- 

 able bird, the Hoatzin {Opisthocovms cristatus), a native of 



