Febbuabt 32, 1907] 



SCIENCE 



313 



days of May find a cloud of marsh mosqui- 

 toes sweeping inland. 



As the marshes are usually waterlogged in 

 early spring- and every pool clean up to the 

 highland holds water, the hibernating eggs 

 hatch in large proportion and the broods are 



An interesting question arises here. The 

 migrants are almost exclusively sterile 

 females : the eggs from which many of them 

 hatch have been on the marsh from early the 

 year before, ready to hatch when opportunity 

 offered. Is there any relation between the age 

 <^ of the egg and the sterility of the females 



resulting from them? The matter will not 

 be easy to demonstrate because of the difficulty 

 of securing pairings in confinement. 



John B. Smith 



color inheritance in mammals 

 Professor Castle's interesting article in 

 Science of January 25 clears up an important 

 point, and renders it possible to explain cer- 

 tain phases of color inheritance in swine and 

 in cattle. For the most part, his factor A, 

 which determines the arrangement of pigment 

 giving the agouti color, seems to be wanting 

 in these two classes of domesticated animals. 

 Perhaps it has been lost. It seems to be 

 present in the wild boar of Europe, which has 

 been used in breeding experiment by Mr. Q. I. 

 Simpson, whose work has furnished important 

 data for the elucidation of color inheritance 

 in swine. In a few instances there is a tend- 

 ency in certain breeds of swine for red pig- 

 ment to predominate near the extremities of 

 hairs ; in the Berkshire breed occasional in- 

 dividuals show this tendency, and I have seen 

 the same in crosses between this breed and 

 Hampshires. The tendency is never well 

 marked, so that in these animals the function 

 A is presumably present in a weakened condi- 

 tion. 



For the most part black and red in swine 

 and cattle evidently behave just as they do in 

 guinea-pigs. Aberdeen-Angus (black) cattle 

 crossed on Herefords (red and white) give 

 blacks. The heterozygotes bred back to Here- 

 fords give blacks and reds in approximately 

 equal numbers. In swine, red and black each 



appear to present more than one type, and the 

 various reds and blacks do not behave quite 

 the same. Tamworths, a red breed of swine, 

 present at least two distinguishable forms of 

 red, namely, light red and dark red. The light 

 becomes lighter with age, and the dark darker. 

 Light is also dominant to dark. When light 

 red is crossed on Chester white the progeny is 

 red roan. Dark red crossed on Chester white 

 gives clear white. 



Most black breeds of swine, when crossed 

 with Tamworths or Duroe- Jersey (both red), 

 give black and red spotted, but Hampshires 

 (black with white belt) crossed with red give 

 the Hampshire coloring. This shows that 

 Hampshire black and Berkshire black differ. 



It is highly significant that the same color 

 factors should exist (apparently) in guinea- 

 pigs, rats, mice, rabbits, swine and cattle. 

 This fact may be of great service in breeding 

 fixed color types in farm animals. 



Professor Castle's clear explanation of color 

 types in Guinea pigs will doubtless aid greatly 

 in comprehending the data on color inherit- 

 ance in swine which the committee on animal 

 hybrids is collecting for the American Breeders' 

 Association. 



The object of this communication is not, 

 however, to call attention to the parallel in 

 color factors in different classes of mammals; 

 for there is not at hand sufficient data to 

 demonstrate a complete parallel. It is rather 

 to call attention to a simple method of ex- 

 pressing the allelomorphic constitution of 

 organisms, and one which renders it easy, 

 when this constitution is known, to display the 

 necessary results of a given line of breeding. 

 We may use Professor Castle's data in illus- 

 trating the method. 



The allelomorphic formula of a homozygous 

 individual may be represented by A A, BB, 

 CC, etc. The gametes produced by such an' 

 individual would be ABO, etc. Letting O 

 stand for the factor which determines the 

 agouti color, Bl for black, and R for red pig- 

 ment, and letting A stand for the absence of 

 G, B for the absence of Bl, and C for the 

 absence of E, the formulae for the several types 

 of color discussed by Professor Castle would 

 be: 



