Organic Evolution. 225 



Eomanes appeals to a gradual failure of heredity, apart 

 from intercrossing, to explain the diminution of disused 

 organs. 



That a variation strongly developed in both parents is 

 apt to be augmented in the offspring is commonly believed 

 by breeders. Darwin was assured that to get a good 

 jonquil-coloured canary it does not answer to pair two 

 jonquils, as the colour then comes out too strong, or is 

 even brown. Moreover,* " if two crested canaries are paired, 

 the young birds rarely inherit this character ; for in crested 

 birds a narrow space of bare skin is left on the back of the 

 head, where the feathers are upturned to form the crest, 

 and, when both parents are thus characterized, the bare- 

 ness becomes excessive, and the crest itself fails to be 

 developed." 



On the whole, it would seem that variations may either 

 be neutralized or augmented in inheritance ; but the deter- 

 mining causes are not well understood. 



Another fact to be noticed with regard to the inheritance 

 of variations is that some characters blend in the offspring, 

 while others apparently fail to do so. Mr. Francis Galton,t 

 speaking of human characters, gives the colour of the skin 

 as an instance of the former, that of the eyes as an 

 example of the latter. If a negro marries a white woman, 

 the offspring are mulattoes. But the children of a light- 

 eyed father and a dark-eyed mother are either light-eyed 

 or dark-eyed. Their eyes do not present a blended tint. 

 Among animals the colour of the hair or feathers is often a 

 mean or blended tint ; but not always. Darwin gives the 

 case of the pairing of grey and white mice, the offspring of 

 which are not whitish-grey, but piebald. If you cross a 

 white and a black game bird, the offspring are either black 

 or white, neither grey nor piebald. Sir E. Heron crossed 

 white, black, brown, and fawn-coloured Angora rabbits, and 

 never once got these colours mingled in the same animal, 

 but often all four colours in the same litter. He also 



* Darwin, " Animals and Plants under Domestication," vol, i. p. 465. 

 t " Natural Inheritance," p. 12. 



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