HO ANNALS NEW YORK ACADEMY OF SCIENCES 



Two questions arise in this connection. The determiner for chocolate 

 is not represented in the presence or absence scheme, since it has never 

 been found absent — i. e., no white mice have been recorded from which 

 all determiners are absent. Such a mouse would be represented by C g b 

 ch. Why, it may be asked, is chocolate excluded from the presence or 

 absence relation? If the chocolate determiner is equivalent to the color 

 producer C, then it too might be absent from some albinos (or from all) ; 

 yet it can be shown that albinos that do not carry other factors carry 

 chocolate, which is contradictory to the assumption. It may be claimed, 

 however, that the chocolate factor has never dropped out in the past; 

 hence its presence in all mice and hence the impossibility of treating it 

 on the presence or absence scheme. Such an interpretation is logical at 

 least. 



In treating the heredity of color in guinea-pigs and rabbits, Castle 

 considers gray as the result of the presence of a ticking factor. In these 

 rodents the gray or agouti may be produced by crossing a black and a 

 red (yellow) individual. Only certain blacks and reds give the result. 

 Castle concludes that some blacks and some reds contain the ticking fac- 

 tor. So long as only one color is present, either black or red, the action of 

 the ticking factor is rendered impossible, since it takes at least two factors 

 to produce the stratified layers. Hence a black animal with the ticking 

 factor is still black, and so is a red only red, but when combined, the 

 presence of red and black and the ticking factor gives again the agouti; 

 but it is not clear why a black animal with the ticking factor should not 

 have the outer ends of the hair (where the red lies in the ticked hair) 

 colorless and the base black. This condition actually exists in the white 

 belly of my wild sports. On the other hand, yellow mice do carry the 

 ticking factor, and yet the hair is uniformly or at least continuously 

 colored yellow, although here too some of my yellow mice with white 

 bellies have a white tip and a yellow base to each hair. If the red guinea- 

 pig is equivalent to the yellow mouse, it may be that the ticking factor 

 can be carried by this type alone and not by the blacks. This view would 

 make the two groups conform, but Castle's evidence seems to show that a 

 yellow that gives agouti with one black may not do so with another. If 

 his cases are sufficiently numerous to show that this is not an accidental 

 result owing to his reds being heterozygous for G, then the suggestion 

 here offered is unavailing. 



In mice, I have found clear evidence that black and chocolate may be 

 stratified to produce a resemblance to gray. Such cases clearly show that 

 in these animals the factor for ticking may be present and effective in 

 the absence of yellow. To prove that this is due to a true ticking com- 



