Botany and Zoology. 323 
the most opposite effects. The result of all these experiments was 
to show that the color influence does act on some element of the 
larval skin, and that the larger the area of skin exposed to any 
one color the more does the pupa follow its influence. Parti- 
colored pup were not obtained, thus probably pointing toward 
the action of the nervous sy stem rather than toward the direct 
action of light on or through the skin itself. 
(6.) The ~ Nature of the effects produced.—The coloring mat- 
ter of the dark pupz is contained i in a thin superficial layer “of the 
cuticle; below this is a thicker layer divided into exceedingly 
delicate lamelle between which fluids are present, and the latter 
form the thin plates which, by causing interference of light, pro- 
duce the brilliant metallic appearance. The thinner upper layer 
being dark, acts as a screen in the dark pup. Precisely the 
same metailic appearances are caused by the films of air between 
the thin plates of glass which are formed on the surface of bottles 
long exposed to earth and moisture. Both have the same spec- 
troscopic characters and the same transmitted colors (comple-— 
mentary to those seen by reflection). The brilliancy of the cuticle 
can be preserved in spirit for any length of time; it disappears 
on drying, but can be renewed on wetting (this had been pre- 
viously known), and the colors are seen to change during the 
process of drying, and when the cuticle is pressed, for the films 
are thus made thinner. The same lamellated layer exists in non- 
metallic pupe, and is used as a reflector for transparent coloring 
matter contained in its outer lamelle. Thus the structure which 
rendered possible the brilliant effects due to interference, probably 
existed long before these special effects were obtained, and was 
used for a different purpose. 
The Biological Value of the Gilded Appearance.—lt is 
probable that the gilded pupe of Vanesside resemble glittering 
minerals such as mica (which is very common in many places) ; 
their shape is very angular, and like that of minerals: conversely 
the gray pupz resemble gray and weathered rock-surfaces, and the 
two conditions of rock would themselves act as a stimulus for the 
production of pupz of corresponding color. The power was 
probably gained in some dry hot country, where mineral surfaces 
do not weather quickly. Once formed it may be used for other 
purposes, and in certain species is probably a warning to the 
enemies that the insect is inedible. It is interesting to note how 
the Vanessidz, primarily colored so as to resemble mineral sur- 
roundings, are modified for pupation on plants. Thus Vanessa 
Io has a green form which is produced among leaves; V. atalanta 
has no green form, and spins together the leaves for concealment, 
but both these species commonly pupate freely exposed on mineral 
surfaces; V. urtice has neither the green form nor the habit, and 
it has a strong disinclination to pupate on its food plant, as many” 
observations concurred in proving. 
Ill Experiments upon Vanessa atalanta.—This species was 
also made brilliantly golden or dark-colored by the use of appro- 
priate surroundings in “the larval condition. 
