34 



TYPES OF MENDELIAN HEREDITY 



rear margin of the scutellum, point constantly in an 

 abnormal direction in club stock. The head of club 

 flies is often flattened, the eyes are smaller, and the 

 thorax and abdomen are somewhat distorted. Here 

 we have an example of a single germinal difference, 

 the factor for club, producing several distinct effects, 



Fic. 18. — Rudimentary wing (to left), and truncate wing (to right). 



some of which are constant features of the stock, while 

 others are occasional or variable. 



Another and similar example is found in the rudi- 

 mentary winged flies (Fig. 18, a) . The wing is usually 

 shorter than the abdomen, but may be longer and even 

 approach the normal wing in length and shape. The 



