DUCKS' LEGS AND WINGS. 57 



inheritance. Thus according to Darwin's tables 

 of comparative weights and measurements * the 

 leg-bones of the Penguin duck have slightly 

 diminished in length, although they have in- 

 creased 39 per cent, in weight. Relatively to 

 the weight of the skeleton, the leg-bones have 

 shortened in the tame breeds of ducks by over 

 5 per cent, (and in two breeds by over 8 per cent.) 

 although they have increased more than 28 per 

 cent, in proportional weight. 2 How can increased 

 use simultaneously shorten and thicken these bones ? 

 If the relative shortening is attributed to a heavier 



1 Variation of Animals and Plants under Domestication, i. 299- 

 301. 



2 To keep pace with this lateral increase in weight, the leg-bones 

 should have lengthened considerably so that their total deficiency 

 in proportional length is 17 per cent., a changed proportion which 

 being linear is more excessive than the increase of weight by 

 28 per cent. So marked is the effect of the combined thickening 

 and shortening that in the Aylesbury breed which is the most 

 typically representative one the leg-bones have become 70 per cent, 

 heavier than they should be if their thickness had continued to be 

 proportional to their length. 



