22S PHYSIOLOGICAL GENETICS 



3. Special Patterns Superimposed upon the General Pat- 

 tern (Secondary Tertiary, Etc., Patterns;. Two examples will 

 show what is meanl by the foregoing heading. The general 

 pattern of a Drosophila wing is given by the arrangement of 

 veins and spaces between the veins; form and arrangement of 

 hairs; and the typical proportions, shapes, and curvatures of the 

 wing. In the series of mutants of the vestigial or beadex type, 

 or similar series, this primary pattern of the wing is not affected 

 or only as far as certain regulations and readjustments are 

 necessitated locally as a consequence of the abnormal develop- 

 ment. But an additional new pattern is created, the typical 

 shapes of the partly destroyed, scalloped wings in different 

 members of the series. For a second example: in the gypsy 

 moth or Promethea moth, female and male wings have essentially 

 the same primary pattern of bands and spots. But in the 

 male, this pattern is overlaid by a dark pigment covering more 

 or less the primary pattern. We consider these types first 

 because they are simpler and also better known genetically. 



If we look at a series of mutants of the vestigial series in 

 Drosophila, we find a definite pattern in each, e.g., the pattern 

 type Notched or Strap (see Fig. 19). These patterns are char- 

 acterized by the following features. 



1. A certain regularity is observed if a series of stages is 

 compared. The scalloping begins at the tip of the wing; it 

 destroys large parts of the wing before the alula and posterior 

 cell are affected ; it destroys the central part of the wing along its 

 entire length last, beginning at the tip. 



2. There is a certain irregularity: the details of the scalloping 

 are rather variable, and often no two wings exactly alike. The 

 two wings of one individual vary independently in regard to the 

 form of scalloping (not in regard to its amount), and symmetry is 

 reached only in the lowest and the highest grades of scalloping 

 (see, however, page 223). But for a given mutant type the 

 average amount of destroyed area is constant within certain 

 limits. We have already given the interpretation of the phe- 

 nomenon of scalloping as derived from the study of development : 

 an insufficiency of a substance needed for growth or the produc- 

 tion of a lytic substance above a certain threshold produces the 

 degeneration that leads to scalloping. If we consider, now, the 

 pattern according to which the different effects occur from nick 



