GENERAL INTRODUCTION. XXll. 



Darwin, Tegetmeier, and other naturalists, and by a host 

 of fanciers. These experiments are especially interesting 

 to biologists, because they point to the conclusion that 

 the crossing of extreme forms leads to reversion towards 

 a remote ancestor — in this case to the wild rock-pigeon, 

 GoJumha livia. But in addition to this a number of 

 other deductions have been made. It has been inferred, 

 e. g., that it is extremely difficult to eradicate blue when it 

 appears in any strain, and that some breeds are more pre- 

 potent than others. 



As I shall have to refer frequently to the wild rock- 

 pigeon, I may here quote Darwin's short but very ac- 

 curate description of its coloration. He says, " The 

 wild rock-pigeon is of a slaty-blue colour ; the wings are 

 crossed by two bars ; the croup varies in colour, being 

 generally white in the pigeon of Europe, and blue in that 

 of India ; the tail has a black bar close to the end, and 

 the outer webs of the outer tail feathers are edged with 

 white except near the tips."* 



Darwin found that when different varieties were 

 crossed, the offspring often in the colour of the wings 

 and tail or in some other respects resembled the blue 

 rock, and in one instance by crossing a barb-fantail ? 

 with a barb-spot c^^ he produced a bird " which was 

 hardly distinguishable from the wild Shetland species." 

 It only appeared to differ in having the head tinted with 

 red, and like the stomach of a paler blue colour, t 



Weismann, in referring to this experiment, says, 

 ''These breeds [the barb, fantail, and spot], as is well 

 known, differ from the wild pigeon in colour as in many 

 other details, such as the length of the beak and number 

 of tail feathers ; and it would therefore be interesting 

 to ascertain whether these racial characters had all dis- 

 appeared in the grandchild, and had been transformed 

 into the corresponding characters of the wild species. 

 Were this so the reversion might be considered complete. 

 . . . Unfortunately Darwin leaves this point untouched, 



* ' Animals and Plants,' vol. i, p. 204. 

 t Ibid., vol. i, p. 210. 



