254 Heredity. 



changes through which its ancestors have passed, sub- 

 stantially in the order in which they first appeared, it 

 follows that, in cases where the sexes are unlike, the one 

 which is most different from the young is the one which 

 has varied. Now, it is only necessary to compare the 

 nearly full-grown young of our domestic fowls with the 

 adult cock and hen, to perceive that the adult hen agrees 

 with the young of both sexes in lacking such male char- 

 acteristics as the highly ornamented tail-feathers, the 

 brilliant plumage, the distended comb, the spurs, and 

 the capacity to crow. Countless similar illustrations 

 might be given to show the great tendency of the male 

 to vary, but the above are sufficient for the purposes of 

 our argument. As both sexes usually retain the more 

 general specific and generic characteristics, and are alike 

 as far as these are concerned, it is a little more difficult 

 to show the conservative constitution of the female than 

 it is to prove the male tendency to vary. Among the 

 Barnacles there are a few species the males and females 

 of which differ remarkably. The female is an ordinary 

 barnacle, with all the peculiarities of the group fully 

 developed, while the male is a small parasite upon the 

 body of the female, and is so different from the female 

 of its own species, and from all ordinary barnacles, that 

 no one would ever recognize, in the adult male, any 

 affinity whatever to its closest allies. All of the heredi- 

 tary race characteristics are wanting: the limbs, diges- 

 tive organs, and most of the muscles and nerves have 

 disappeared, as they are not needed by a parasitic ani- 

 mal; and the male is little more than a reproductive 

 organ attached to the body of the female. It is only 

 when the development of the male is studied that we 

 obtain any proof of its specific identity with the female. 

 The young of both sexes are alike, and the developing 



