152 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



If the bands continue to become more and more bent outwardly and the 

 fascise between them gradually narrowed, forms of the type of fragilella (Fig. 3) 

 will be produced. If now the action of the third law comes into play, the 

 outer edges of the bands on the margins will move toward the base; if the 

 extremities of the bands are extended toward the base at the same rate, very 

 acutely angled fascise will result, as in celtifoliella (Fig. 4) . 



If the extension of the ground color toward the base in Band VI has taken 

 place rapidly, there is an entire obliteration of white between V and VI, which 

 then form a single uniformly colored band. In tritcenianella (Fig. 5), affinis 

 (Fig. 6) and ostensackenella (Fig. 7), this has occurred, Bands II, III and 

 IV remaining nearly straight. In mariceella (Fig. 8), these bands have 

 become bent outwardly. In ostensackenella, while the bands have remained 

 straight, there has been a very decided advance and specialization in other 

 directions; namely, in the structural modification of the scales forming the 

 fascise and spots and in the darkening of the base of the wing into a deep brown 

 except near the base of the dorsum. There has also been considerable modi- 

 fication in the larva, which has become more flattened and in which the sides 

 of the segments project more prominently than usual. It also deviates from 

 the typical habits of the genus in that it leaves the mine to pupate. 



We may regard Porphyrosela as having originated from an ancestor with 

 this type of marking. The recent origin of the species within it (Fig. 9) is 

 indicated by the deep ground color, dark margins on either side of the white 

 fascise and the structural modification of the white and the purple scales. 



If the extension distally of each of the bands along the cell has continued 

 until it has reached the band beyond and the inner extremities of the bands 

 have been produced basally at a slower rate, the result is the production of pairs 

 of opposite white streaks. 



In auTonitens (Fig. 10), it is probable that the fascise were considerably 

 narrowed before these processes began, thus accounting for the almost per- 

 pendicular position of the white streaks. 



In the remaining groups of species, these processes began early and the 

 pairs of streaks are more or less oblique. There is first produced a form in 

 which the ground color is blocked out as in argentinotella (Fig. 11). Occi- 

 tanica (Fig. 12) is derived from argentinotella by the obliteration of the first, 

 fourth and fifth costal streaks. 



If now a movement of the extremities of each band toward the base is 

 accompanied by a corresponding extension of the extremities of the band beyond 

 it toward the base, very obhque white streaks result. Where these movements 

 have taken place at an approximately equal rate in all of the bands, forms such 

 as leucothorax (Fig. 13) will be produced. The outer edge of Band II on the 

 costa has been retracted completely to the base so that the first white costal 

 streak begins at the base. This species furnishes further evidence of the long 

 continuance of evolution by the well developed apical spot. 



