Embryology 335 



essential. They may have a smaller and degenerate form 

 of any feature not continuing necessary. For example 

 the wings of domestic fowls, may be produced smaller and 

 degenerate, in offspring of parents who never use those 

 wings, and if no loss arises from that degeneracy it will 

 continue. But still wings will persist many generations. 

 They have been the valuable heritage of the creature so 

 long, that early in the development of the chick from the 

 egg, the wings began to grow, representing the proportionate 

 earliness in the evolution of the race which acquired wings, 

 and evolved them into strong and large organs by necessity 

 for self-preservation. What has so long been cultivated will 

 require corresponding length of time to eliminate. Yet it 

 is only a matter of time. If the wings are entirely disused 

 they will in time disappear. Or, if useless as wings, the 

 limbs may be converted to such other use as is found and 

 proved beneficial. Many new features appear by this trans- 

 formation of very old ones. The feet of the duck have 

 become swimming appliances and in some diving fowl even 

 the wings have been adapted to use as fins for swimming 

 under the surface. 



But when we consider a very recently attained character, 

 as for example a new color of the plumage, or even a new 

 shape and size of feathers, or of feet, or of claws, we find 

 even greater adaptability. The offspring may vary con- 

 siderably from the last parent. A condition of variability 

 arises when in cessation of need of some character, there 

 is no corresponding new necessity settled. There may be 

 then a relaxing of recent control of heredity, with much 

 unregulated variation, instead of an addition or a substitu- 



