132 ORIGIN OF SOMATIC 



As it seemed possible that there was some natural 

 congenital difference in growth of feathers between 

 cocks A and B, I commenced early in March 1903 to 

 pull and stroke the feathers of the left side only in 

 cock A, leaving those of the right side untouched. 

 On 30th July on the left side the central rectrix and 

 the first and second posterior coverts were still 

 growing, on the right side the central rectrix was also 

 growing, but the first and second posterior coverts 

 had ceased growth and formed their quills. The first 

 posterior covert on the left or pulled side was 3 inches 

 longer than that of the right. The second posterior 

 covert on the left side was still longer. The first and 

 second posterior coverts of left side did not cease 

 growth till 26th August. On 2nd September the 

 left central rectrix was almost at the end of its 

 growth, the right had ceased to grow a little before. 

 The left was about an inch longer than the right. 

 Thus both in length and in duration of growth the 

 feathers of the pulled side were longer than those of 

 the right, and this was the result of treatment con- 

 tinued only six months, and commenced some 

 months after the feathers had begun to grow. I 

 have no doubt, however, that the pulling out of the 

 feather as soon as it shows signs of forming quill, so 

 that its successor at once grows again, is even more 

 important in producing the great length of feather 

 than the stroking of the feather itself. 



In this case, then, there is no doubt (a) that 

 the long-tailed birds are artificially treated with the 

 utmost care and ingenuity by the Japanese, who 

 produced them; (b) that the mechanical stimulus 

 in my experiments did cause the feathers to grow 

 for a longer period and attain greater length; 



