INDIVIDUATION— FORMATION OF PATTERN AND SHAPE 425 



of the wing; the effect on the pattern formation must be brought about 

 by altering the reaction of the material to effects of the wing boundary, 

 rather than by altering the boundary itself. Other cases, however, suggest 

 that the amount and shape of the material available to form the wing 

 may have an effect on the pattern of venation. For instance, in dachs the 

 longitudinal veins are splayed apart and at the same time the wing is 



Figure 204 



^^.^^-'^ontrolled modifications of the pattern of wing venation in Droso- 

 phila.Ina, h, c, d, e the mutant wing is drawn in a fiillUne, superposed on a 

 dotted drawing of a normal wing; a, in shifted-2 the longitudinal veins are 

 pinched together; h, in broad, the wing blade is relatively broader than nor- 

 mal and the veins diverge at a greater angle; c, veinlet may remove a con- 

 siderable part of the distal region of the veins, and the posterior cross-vein 

 IS moved to fit; d, cubitus ititerruptus removes the distal part of the fourth 

 vem, and the fifth then shifts upwards ; e, dachs produces a short square wing, 

 m which the veins diverge at a greater angle than normal;/, the dachsous 

 wmg IS large and the veins diverge at a large angle, notice also the cross- 

 veins; g, much-altered venation when the wing shape is highly abnormal 

 {dachsous-fourjointed-plexus); h, small mirror-image twin wing produced by 

 blot. (After Waddington 1940, etc.) 



