410 PROGRESS OF SCIENCE IN THE CENTURY. 



found within the verifiable family, within the breed, 

 within the species, or even in a presumed ancestral 

 species. 



The best illustrations of reversion are furnished 

 by hybrids. Thus in one of Prof. Cossar Ewart's 

 experiments a pure white f antail cock pigeon, of old- 

 established breed, which in colour had proved itself 

 prepotent over a blue pouter, was mated with a cross 

 previously made between an owl and an archangel, 

 which was far more of an owl than an archangel. 

 The result was a couple of fantail-owl-archangel 

 crosses, one resembling the Shetland rock-pigeon, and 

 the other the blue rock of India. ~Not only in 

 colour, but in shape, attitude, and movements there 

 was an almost complete reversion to the form which 

 is believed to be ancestral to all the domestic pigeons. 

 The only marked difference was a slight arching of 

 the tail. Similar results were got with fowls and 

 rabbits. 



Such facts lead us to the theory that characters 

 may lie latent for a generation or for generations, 

 or in other words that certain potentialities or 

 initiatives which form part of the heritage may re- 

 main unexpressed for lack of the appropriate liberat- 

 ing stimulus, or for other reasons, or may have their 

 normal expressions disguised. But it does not follow 

 that the reappearance of an ancestral character not 

 seen in the parents is necessarily due to the reasser- 

 tion of latent elements in the inheritance. It may be 

 a case of ordinary regression; it may be a case of 

 arrested development; it may be an extreme varia- 

 tion whose resemblance to an ancestral charac- 

 teristic is a coincidence; it may be an individually 

 acquired modification, reproduced apart from inherit- 



