OF MUTANT CHARACTERS. 161 



70 degrees. It is this typical curvature of the wing that is used in 

 classification, though, as is usually the case with mutations, there are 

 present various associated or accessory characteristics which are of 

 value, but which in this case must not be relied on over much. Thus, 

 the upper lamina of the wing is frequently corrugated transversely, 

 which is probably the cause of the curvature, though it may be the 

 result. The "inner" side of the wing (posterior margin) is often more 

 strongly curved than the ' 'outer," and in these cases the tips of the 

 wing have a slight oblique slant "outward." The jaunty wings have 

 a tendency to be spread farther apart than normal, though the amount 

 of divergence is slight. In color the wings are a clear gray, slightly 

 darker than normal, and are of strong, thick texture, not flimsy, as in 

 certain other wing mutations. The body-color also is probably a trifle 

 darker than normal. All of these accessory characters are so slight 

 that they would ordinarily be unnoticed. 



A "MUTATING PERIOD" FOR JAUNTY. 



Soon after the discovery of jaunty, -a character which seemed to be 

 the same as jaunty was found (May 1912) by Morgan to be present in 

 the F 2 of a cross of yellow abnormal to white. In rapid succession 

 (May, June, July, 1912) jaunty or jaunty-like characters were dis- 

 covered in some half dozen stocks or experiments, so that the idea of a 

 "mutating period" for jaunty became current. It is possible that 

 the jaunty mutation did occur on more than one occasion ; certainly we 

 were unable to trace any recent or probable connection between three 

 of these appearances of jaunty, namely, the two just given and a case 

 which appeared in the crosses by Bridges of purple vestigial to wild. 

 There are plenty of proved cases in which a mutant character (or an 

 undistinguished allelomorph) has appeared on a second or third occa- 

 sion, and there is no a priori reason why these several mutations might 

 not occur at about the same time. But there are several points to be 

 guarded against before accepting any supposed recurrence of a muta- 

 tion as genuine. For example, it is surprising through how many gen- 

 erations a recessive will persist in a mass stock even when the character 

 is poorly viable and is selected against in a rough fashion. Thus, the 

 wing mutation "spread" occasionally crops out in the black-plexus 

 stock where it has been carried along "under the surface" for three 

 years, some 75 generations. Any cross made with the black-plexus 

 stock is liable to transmit the spread also, so that a recent case of 

 spread reappearance was finally run to earth as coming from a black- 

 plexus cross made some six months previously. Cases like this are 

 all too frequent and emphasize the value of strict pedigrees and of 

 "cleaned up" stocks. Another point is the pyschological one of 

 recognition. One can fail to see a mutation which has been contin- 

 ually present in flies examined for some generations, and which is so 



