144 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
black, without passing through the intermediate yellowish and brownish shades. 
The tendency for dark pigment to develop along the edges of bands adjacent to 
unpigmented areas is exemplified in this group also, with this difference, however, 
that it appears first along the inner edge of aband. When dark pigment develops 
in addition along the outer edge, it appears at a later period. The converse is 
true in the first division of the genus; the dark margin appears earlier on the 
outer side of a band. I сап offer no explanation of the original cause of the 
difference in direction of development; the result in either case seems to be the 
expression of the same general tendency in development, acting, however, with 
different degrees of intensity on either side of a band. It would seem that the 
development of unusually dark pigment on one side of a band—the acceleration 
of chemical processes over a localized area—retards development on the other 
side. 
The ontogeny within this division affords very little evidence of the operation 
of the first two processes of evolution defined earlier in this discussion. However, 
the shape of the bands and the separation of the white fascize into opposite spots, 
with the total obliteration of some of the spots, is sufficient proof that these forces 
have acted during the evolution of the species. 
L. hamadryadella (Fig. 77, Pl. IV) alone, of those observed, shows the out- 
ward prolongation of the middle of a band; the gradual extension distally of 
the dark dusting between the dorsal and costal portions of Band V + VI and 
its final contact with the apical dusting (Figs. 22, 23) is an example of the 
working of this law. The third law postulated to explain the displacement of 
oblique streaks toward the base receives decisive confirmation from the adult 
markings of the same species. A narrow line of scales crosses the wing beyond 
the yellow portions of each of Bands II, III and IV, being separated from them 
by white. These scales occupy positions corresponding to the outer margins of 
these bands; ontogenetically, the dark pigment develops in them after it has 
appeared on the inner margins of these bands. The conclusion is apparent that 
these lines of scales mark the earlier phylogenetic limits of these bands. The 
bands have shrunk away, most rapidly on the costa and dorsum, leaving behind 
them the margins as visible evidences of the process. 
In L. tiliacella (Fig. 7), which, from its conservation of the greatest 
number of bands in a primitive straight condition, the very pale ground color 
and the entire absence of any dark scales in some of the bands, may be regarded 
as the most primitive of the American species, there is a difference in the time 
of appearance of the bands. In the more advanced species, the bands appear 
at the same time. Evidently, then, in the higher species, there is a hastening 
and crowding together of the earlier stages, so that the bands which formerly 
appeared in sequence now appear contemporaneously. Those in the apex of 
the wing, which have experienced the least modification during the phylogenetic 
development of the species, alone recapitulate the racial history during their 
ontogenetic development. 
