Referate. ig I 



these factors, e. g. IwXYZ, IVVXyz, IWxyz, differ visibly in the amount of 

 pigmented area of the coat, it is equally certain that all such animals 

 would have been completely pigmented if only they had had L in their 

 formula. Therefore the genetic difference between such animals as LWxyz. 

 LWXyz and LWXYZ would not result in a visible difference, the presence 

 or absence of these factors, W, X, Y, Z, being as little noticeable in mice 

 having L (solidcoloured) as in albinos. 



We can now see that, when we cross a" spotted animal with little 

 colour, to a solidcoloured one, it will depend upon the genetic constitution 

 of this last one, as to whether the spotted young produced in the second 

 generation of the cross, will be all as light as the original spotted, or of 

 difierent type, some being darker or lighter. 



If our spotted animal was IWxyz, and our solidcoloured one was 

 LWXYZ, it stands to reason that some of the spotted ones in F.. will 

 have the factors X, Y and Z, which were introduced by the solid-coloured 

 parent, in different combinations, and therefore will be marked with more 

 colour. If in another case, the genetic formulae of the spotted and the 

 solidcoloured animal will be identical, with the exception ot the possession 

 or not of L, it stands to reason that all the spotted ones in F-, will be 

 of the same kind as the original spotted one. Or even, if a dark spotted 

 animal is mated to a solidcoloured one which has less of these factors 

 WXYZ than the spotted one, for instance when an Lwxyz animal is mated 

 to an IWXYz one, there will in F.> be produced spotted young, with less 

 pigmented area than the spotted parent, for instance IWxyz, or IWXyz ones. 



I have found a case of this latter kind in my experiments with mice. 

 From a mating of a solid black male, to a female, nearly solid black, with 

 the exception of a narrow band around the body and white feet and 

 tailtip. there were born colid- coloured young who, mated inter se produced 

 at least two young, spotted with very much white. I am working out 

 this question with rats now, and hope to get to know these factors 

 more fully. 



Of course, only in the case where, by chance, the solidcoloured parent 

 has more of these factors X, Y, Z, etc. than the spotted one, can the 

 result be such as to give the idea of a contamination of gametes. I do 

 not think we need to assume lor the expanation of the facts found by 

 Morgan, an}' special hypothesis, such as the one he offers, that the '"spotted 

 coat represents a process which occurs at the early cleavage of the egg". 



In comparing the difference between -potted and solid- coloured 

 coat, to that between fully pigmented and ticked hair, M. assumes that 

 the "ticking factor" has the same theoretical value as the "spotting factor". 

 But, whatever be the nature of the genetic factors, it will never do to hold 

 that these two things can be in any way analogous, for the reason that 

 the ticking of the hair in agouti animals as compared to the absence of 

 ticking in that of e. g. black, is caused by the presence of a well-studied 

 factor, whereas the "spotting" of the coat results from the absence of one 

 or more genetic factors present in solid coloured animals. 



In breeding spotted animals to his white-bellied agouti sports, M. could 

 show that the factors influencing the destribution of the spots are inde- 

 pcndant of the one which makes the difference between whitebellied and 

 gray-bellied animals. 



In his chapter on crosses between black spotted waltzers and mice 

 with chocolate coat, M. raises the question as to the possibility of consi- 

 dering these waltzing mice as belonging to a different race or species from 



