98 CROSSING. 



fifty, because it would give us a chance to study the relations 

 of genes 4, 28, 34, 36 and 329 without being detracted by S3an- 

 bois which stand for fantastic characters that result in certain 

 types in the presence, or even in the absence, of such genes. 



The behaviour of the genes in heredity, their relations dur- 

 ing segregation are things to be studied by themselves. These 

 are the things which readers of papers on Drosophila are in- 

 terested in. The other geneticians, reading about this work are, 

 for the time being, content to take the specialists word for 

 the analysis of the counts of his flies. 



On the other hand the specialists working with the material 

 have to know, what each gene stands for. From personal ex- 

 perience we know, that bare niunbers very rapidly associate 

 themselves with memories of peculiarities of the material. In 

 recalling our work with squashes the number 161 brings to 

 our mind a particular t5^e just as clearly as the name "Mi- 

 racle" does, and in our pedigrees of our mice numbers 2112 

 of the old series and 147 and 148 of the new series recall par- 

 ticular animals quite distinctly. 



We should clearly distinguish between these tw6 desiderata, 

 making the data easy to work with for the experimentators, 

 and making them intelligible for the other geneticians, who 

 are expected to read them. 



If we know a gene which is present in black animals and 

 absent from brown ones, and a second one which is present 

 in black-eyed but not in pink-eyed, we can study the relation 

 of these genes to each other just as easily, if we call them A 

 and £ or 15 and 16, as if we called them Bl and Bl^. If we call 

 them A and B the facts are intelligible to everybody. If we 

 call the first one Bl, this abbreviation suggests "black" to the 

 man who uses the abbreviation. A French author would call 

 this gene N, a Scandinavian or German would prefer to call 

 it S, we Hollanders should call it Z. 



But, after all, there is no real blackness anywhere about 

 this gene. It does ilot regularly produce blackness. In a very 

 definite combination of a dozen or so other genes which we 



