April 5, 1907] 



SCIENCE 



543 



blacks and one gives 100 per cent, belts ! 

 Tliese results are in accord with the experience 

 of breeders, and explain this experience com- 

 pletely. 



How shall the breeder proceed to eliminate 

 the undesirable blacks ? If a single dominant 

 unit character were to be bred pure, the way 

 to do this would be to discard both parents 

 when black pigs occur. This would rapidly 

 reduce the number of black pigs produced. 

 But here we desire to perpetuate two dominant 

 characters. The desired result will ultimately 

 be secured by discarding both parents of all 

 black pigs farrowed, but very slowly; for 

 heterozygotes are not always revealed by 

 breeding them together. For instance, types 

 i and c bred together produce only belted pigs. 

 Neither can we test out the heterozygotes by 

 breeding to blacks, for in many cases this type 

 of breeding gives only belts. We can, how- 

 ever, determine whether an individual is homo- 

 zygous by breeding to a breed which possesses 

 neither of the factors F and G. Only type a 

 thus bred will give all belts. But here a diffi- 

 culty arises. One or the other of these fac- 

 tors is present in at least four other breeds. 

 This is demonstrated by the fact that when 

 Tamworths are crossed on Chester whites, and 

 when Duroe-Jerseys are crossed on Yorkshires, 

 the belt sometimes appears in part or all the 

 progeny. It is not yet known whether Berk- 

 shires and Poland Chinas possess either of 

 these factors. 



The presence of the factors F and G in four 

 of our standard breeds accounts fully for the 

 occasional occurrence of ' listed ' (belted) 

 hogs in swine of mixed breding, a not uncom- 

 mon occurrence in sections where mixed 

 breeding is common. 



The fact that some breeds possess the factor 

 F and others the factor G, unsuspected until 

 revealed by the numerous breed crosses made 

 by Mr. Q. I. Simpson, hints at the possibility 

 that at some remote time the ancestors of our 

 domesticated swine were belted after the man- 

 ner of the related Indian tapir, and that the 

 belt disappeared by the gradual weakening of 

 factor F in some cases and of factor G in 

 others. In America, where our swine trace 

 to breeds from all parts of the world, these 



factors have been brought together again, re- 

 newing this striking belt character. It is sug- 

 gested that the Tamworths and Yorkshires 

 probably carry the same factor, these breeds 

 both coming from England. Chester whites 

 and Duroc-Jerseys originated in America, and 

 possibly inherited the other factor from the 

 Chinese hog, which entered into most of our 

 early breeds. 



It is entirely possible that the belt character 

 is more complex than here indicated. How- 

 ever, the difference between belted and black 

 Hampshires evidently relates to two factors 

 only. 



The distribution of black and white in Berk- 

 shires and Poland Chinas is evidently gov- 

 erned in a manner similar to that above as- 

 sumed for Hampshires, though it is not known 

 how many factors are concerned. These two 

 breeds are black with white 'points.' Until 

 recently Poland Chinas were black and white 

 spotted. The presence of a few animals in 

 the breed having the black color with white 

 points furnished the factor or factors that 

 ultimately gave the breed its present color 

 type. 



It is suggested that the arrangement of 

 color on all spotted animals may be governed 

 in some such manner as that here indicated. 

 The presence of several factors having this 

 relation to color distribution, and scattered 

 promiscuously through a spotted breed, would 

 account for observed facts. The tendency for 

 color spots to appear in definite places, as 

 black on the rump in swine having most of the 

 body white, a very persistent tendency, the 

 localization of spots on fox terriers, and the 

 strong tendency for red hairs to appear about 

 the ears of white cattle, aU point in this di- 

 rection. 



W. J. Spillman 



U. S. Depabtment of Agricdltube 



WING VEINS OF INSECTS 



An adequate reply correcting all the mis- 

 statements occurring in the review' in Sci- 

 ence of February 8, of my article on wing 

 veins would be beyond the limits of space 

 available for this article, and I shall have to 



' Pp. 219-229. 



