298 MAINE AGRICULTURAL EXPERIMENT STATION. I915. 



SEVENTEEN YEARS SELECTION OF A CHARACTER 

 SHOWING SEX-LINKED MENDELIAN INHERIT- 

 ANCE.* 



In 1898 there was begun at the Maine Agricultural Experi- 

 ment Station an experiment in breeding Barred Plymouth Rock 

 fowls, having for its purpose the improvement by selection of 

 the character winter egg production. This investigation has 

 continued to the present time. 



The experiment has fallen into three divisions or periods : 

 viz., (i) the period from 1898 to 1907, (2) the period from 1908 

 to 1912, and finally (3) the period from 1912 to date. Detailed 

 reports on the methods of breeding in operation have been pub- 

 lished elsewhere. t For purposes of clear orientation in the 

 present discussion it will be well here briefly to review the facts 

 as to the methods of breeding used in each of the periods. With 

 these facts definitely in mind we may then proceed to an exami- 

 nation of the results. 



I. The Period from i8p8 'to 190/. — During this period the 

 breeding followed the plan outlined at the beginning by Woous 

 and Gowell. Essentially it consisted of the following elements. 



1. Trap-nest record of the performance of each individual 



female. 



2. Selection as breeders of all females which laid more 



than a definite number of eggs (150) in the first lay- 

 ing year. 



3. Selection as breeders of males whose dams had lai 1 



more than another definite number of eggs (200). 



4. The indiscriminate mass breeding, zuitJiout individual 



pedigrees, of all individuals selected as described un- 

 der 2 and 3, and, in consequence, 



*This is an abstract of a paper by Raymond Pearl, having the same 

 title and published in American Naturalist, Vol. XLIX, pp. 595-608. 1915. 



tCf. particularly Woods, C. D., and Gowell, G. M., U. S. Dept. Agr. 

 Bur. Anim. Ind. Bulletin 90, 1906, pp. 42 ; Pearl, R., and Surface, F. M., 

 Ibid. Bulletin no, Part I, 1909, pp. 80; Pearl, Me. Agr. Expt. Stat. Ann. 

 Rept, 191 1, pp. 1 13-176; and Pearl, Jour, Exp. ZooL, Vol. 13, 1912, pp. 

 153-268. 



