434 p. W. WHITING 



This would give a theoretical ratio of 2 sooty (SS.Bb and Ss.Bb), 

 1 sooty black (SS.bb), and 1 black (sS.bb). The expected ratio 

 is 62 sooty, 31 sooty black, and 31 black. 



III. SUMMARY AND GENERAL DISCUSSION 



Genetic work on the Mediterranean flour-moth has been handi- 

 capped by low fertility of the pairs, due for the most part to 

 failure of females to oviposit. 



Variations in size are apparently not hereditar}^ 



Variations in length and divergence of leg spines, as well as 

 abnormalities in external male genitalia, have not been tested 

 genetically. 



Defects in the labial palpi are hereditary but very irregular 

 in appearance and probably much affected by environment. 



The heredity of color variations and of cleft tongue will be 

 discussed below. 



A . The masking of a Mendelian difference by environment 



It has for some time been recognized that the failure of a 

 genetic character difference to appear is not necessarily due to 

 the absence from the germ-plasm of the genetic factor or factors 

 involved. 



Baur ('11) has shown that in Primula sinensis both a genetic 

 factor and certain environmental conditions are necessary for 

 the production of pigment, and in Drosophila Morgan ('15) has 

 demonstrated this for production of abnormal abdomen and 

 Hoge ('15) for supernumerary legs. 



In moths with cleft tongue, maxillae fail to unite for a vari- 

 able part of their length. This abnormality apparently depends 

 for its expression on certain environmental conditions, among 

 which humidity is important. The hereditary basis may be a 

 single factor difference from the normal, but further work will 

 be necessary in order to demonstrate this conclusively. 



