MORGAN, COAT COLORS IN MICE 103 



dence seems peculiarly significant because of the occurrence of a race of 

 domesticated mice that breeds true to this character. The test is even 

 more significant, when we recall that the waltzing habit when induced 

 artificially seems to be permanent. I have kept artificial waltzers for 

 more than a year and at the end of that time they waltzed as well as at 

 first. It seems probable, therefore, that the drug has caused a permanent 

 change in the animal, and since it is known to produce degeneration of 

 certain nerve fibres in man, it seems not unlikely that the effects in mice 

 are of the same nature. Yet, despite the permanency of the effect, the 

 acquired character is not transmitted through the germ cells. 



Dr. Terry has also produced for me a number of waltzing rats by 

 means of larger doses of atoxyl. Unfortunately, none of these have bred 

 when both parents were waltzers. 



Are Black and Chocolate Different Pigments or Stages in the 

 Development of the Same Pigment? 



There are two methods of treating the colors black and chocolate in 

 mice. They are generally considered to be different unit characters and 

 the product of different factors, but I have found some evidence that indi- 

 cates that these two pigments may be intimately related, and I suggest 

 that they may represent different developmental stages of the same 

 process. From this standpoint, black is a further development of the 

 same chemical process that produces chocolate, and since pure black and 

 pure chocolate races exist, there must be some special condition or factor 

 that leads to the further development of chocolate to make a black mouse. 

 Let us represent this higher stage by the symbol M. A black mouse is y 

 therefore, Ch Ch MM, and its gametes are Ch M and Ch M. A chocolate 

 mouse is Ch Ch. When black is mated to chocolate, the hybrid is Ch Ch 

 M, which gives in the next generation three blacks to one chocolate. 

 Similarly when chocolate Ch Ch is crossed to gray (Y Ch) M, the first 

 generation will be gray, and the second will contain gray (including cin- 

 namon agouti), black and chocolate in the proportion 12 : 3 : 1. 



The dilute colors, blue (or dilute black) and silver fawn (or dilute 

 chocolate) require special consideration. Dilute black is not chocolate, 

 as Cuenot supposed, but the dilute effect is due to the sparseness of the 

 black granules. Similarly dilute chocolate owes its peculiarity to the 

 fewness of the chocolate granules, rather than to their weakening. The 

 experiments of Miss P. M. Durham show that the factor producing 

 sparseness in black produces the same effect in chocolate. This factor, S, 

 is not to be confused with the factor M that transforms chocolate to a 

 higher stage — i. e., into black. When dilute black is crossed with choco- 



