Referat e. 



193 



In a special chapter Morgan treats of the ticked hair as a "unit- 

 character" and he shows how this factor which produced this ticking is 

 treated by different authors on the subject. 



M. develops te idea that it is "yellow" which must disappear, if an 

 agouti animal is to become black, not a special "barring" factor. This is 

 of course true in a certain way, a black mouse has no yellow pigment or 

 hardly any. But when we are speaking about these genetic factors we do 

 not identify them with the pigments Ihey "produce", and this factor, 

 which Castle calls the "barring" factor, is a well-known factor, studied in 

 four or five animals, and which by no means in all circumstances makes 

 the coat yellower. 



I would draw attention to the fact that a chemical analysis of the 

 hair of a coloured mouse can in no case be used as a criterium cs to the 

 correctness or otherwise of the genetic formula found to correspond to this 

 colour, for the reason, already given, that these formulae do not tell 

 anything about pigments, but sim{)ly about the genetic factors which 

 cooperate to form, influence or modify this pigments. For example, we 

 know that in a black mouse there must be first a factor which would, if 

 present in a certain combination give yellow colour. Secondly another 

 factor, which, when added to this combination would make the colour 

 brown, and thirdly one which, when added to these two, would make the 

 colour black. 



It was, as I have already pointed out, a great mistake to call these 

 factors "Yellow", "Brown", and "Black" respectively. But, as this has 

 been done by several authors, the unavoidable outcome was, that people 

 did not distinguish between these genetic factors and the three pigments, 

 yellow, brown and black (I have formerly made this same mistake). If 

 these genetic factors were, or stood for, the pigments, Morgan would be 

 right in saying that a black mouse, with the formula YBrBl, should have 

 yellow, brown, and black pigments, and that, if any one of these pigments 

 should be found missing, the genetic formula could not be correct. 



As, however, these factors are in no way representative of the pigments, 

 it may be well conceived that, under the influence of the second factor 

 all the hitherto yellow pigment is transformed into brown, and under the 

 influence of the third, all the brown into black pigment. 



In the conclusion of his paper, Mori;an develops some ideas, which 

 bring him to essentially the same views as to the mode of operation of 

 the genetic factors as are held by Baur and by myself'), namely, that 

 not every genetic factor stands for, and calls into being a definite "unit- 

 character", but that each of these factors influences the development 

 somewhat, and by modifying the course of this development causes the 

 result to be something different from what it should have been without 

 its cooperation, and that the genetic factors cooperate with non-genetic 

 factors and can only act in spezial conibinations of other genetic and non- 

 genetic factors. A. L. Hagedoorn. 



East, E. M. A mendelian interpretation of variation that is apparently con- 

 tinuous. Amer. Natural. XLIV 1910 S. 65—82. 



East, E. M. and Hayes, H. K. Inheritance in maize. Connecticut agri- 

 cultural experiment station bulletin N :r 167 and Contribution from the 



1) Autokatalytical substances the delermin;vnts fur the inheritable 1 

 lloux' Serie Vorträge unj Aufsätze. 191 1. 



Induktive Abstainnumg?!- und Vererbungslehre. VI, 1 3 



