152 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETTS. 
If the bands eontinue to become more and more bent outwardly and the 
fasciæ 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 fasciæ 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 tritenianella (Fig. 5), affinis 
(Fig. 6) and ostensackenella (Fig. 7), this has occurred, Bands II, ПІ and 
IV remaining nearly straight. In marieella (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 
fasciz 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 
fascie 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 auronitens (Fig. 10), it is probable that the fasciæ 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 oblique 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 П 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. 
