MUTATION 69 



says: "During the past four years I have handled 

 and described over 10,000 poultry of known ancestry. 

 Of striking new characters I have observed many, 

 some incompatible with normal existence; others in 

 no way unfitting the individual for continued life. 

 In the egg unhatched I have obtained Siamese twins, 

 pug jaws, and chicks with thigh bones absent. There 

 have been reared chicks with toes grown together 

 by a web, without toenails or with two toenails to 

 a toe ; with five, six, seven, or three toes ; with one 

 wing or both lacking ; with two pairs of spurs ; with- 

 out oil-gland or tail; with neck devoid of feathers; 

 with cerebral hernia and a great crest; with feather 

 shaft recurved, with barbs twisted and dichoto- 

 mously branched or lacking altogether. Of comb 

 alone I have a score of forms. All of these characters 

 have been offered to me without the least effort or 

 conscious selection on my part, and each appeared in 

 the first generation as well-developed peculiarities, 

 and in so far as their inheritance was witnessed, each 

 refused to blend when mated with a dissimilar form." 

 Bateson (1894), in his "Materials for the Study of 

 Variation," gives a detailed list of 886 cases of "dis- 

 continuous variations" among animals, many of which 

 doubtless belong to the category of mutations, al- 

 though several must be placed in the non-inherit- 

 able class of "freaks." 



9. POSSIBLE EXPLANATIONS OF MUTATION 



It is apparent that the causes of mutations, since 

 they occur regardless of the environment, are prob- 



