CROSSING. 97 



does, and does not lead people always to think of the colour 

 black, when they see the symbol Bl, or worse, to think of the 

 gene Bl whenever they see black colour. The most prevalent 

 argument in favor of the use of terms for genes that recal char- 

 racters, is, that it makes the papers on factorial analysis easier 

 to read and understand than those in which the authors follow 

 Mendel's system of denoting genes by non-committal letters of 

 the alphabet or by numerals. This is a question of taste. Person- 

 ally, we find it exceedingly difficult to dig down to the facts 

 hidden under the laborious terminology of the work of the au- 

 thors using this system, even of those authors like Plate and 

 Morgan, who are obviously not themselves confused. And a 

 great number of papers by recent investigators working with 

 Drosophila are so hopelessly confused in their use of such terms 

 as gene, character, locus, mutation, that it is hardly worth 

 while to try to get a picture of what may have happened in the 

 experiments described. 



We cannot help thinking, that an author who consistently 

 writes about a notch gene must eventually come to look upon 

 this gene as upon a determinant for the character, and upon 

 the character as bound up with the gene. 



What we try to study in work of this kind, is after all the 

 mechanism of heredity and segregation, the relation of the 

 different genes to each other. It is possible to read a paper on 

 factorial analysis and to concentrate one's attention upon the 

 mutual relations (linkage, coupling) of six genes called A, B, 

 C, D, E, and F, without verifying at the time in what particu- 

 lar way, and in what combinations these genes demonstrate 

 their presence in the material. Speaking for ourselves we are 

 very much interested in the mutual relations of the very many 

 genes demonstrated by Morgan and his pupils in Drosophila 

 and only very little in the particular characters of the flies 

 which vary certain combinations of these genes. We would 

 be overjoyed, if someone would transpose the facts in some 

 of the most interesting cases and would denote the genes sim- 

 ply by numbers, numbering them from one to four-hundred- 



