OF MUTANT CHARACTERS. 



221 



dachs, is entirely normal in viability. In all other respects dachs is of 

 first rank. Since the character used in classification is the number of 

 joints of the tarsus, there is no masking effect possible with any of the 

 other second-chromosome mutants. The recessiveness of dachs is com- 

 plete, its identification is perfect, and the separations are easy and rapid. 

 The locus of dachs is such that it is the most important connect inp- 

 link between the left end of the chromosome and the securely cstab- 

 hshed and well-mapped region from bkck to the right end of the 

 chromosome. 



