EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 119 
at first, become opaque, yellowish or light drab, beginning first near the base of 
the wing and spreading distalward. Soon spots, stripes and adult markings 
appear, at first proximad, then more and more distad, then between the nervules 
and, last of all, upon the nervules. First, the purely pigmental or chemical 
colors develop, and these are followed by the chemico-physical.”’ 
The principal researches have been those by Schiiffer ('89), Van Bemmelen 
(89), Urech (791), Haase (93), Mayer (796) and most recently by von Linden 
(98, '02). The principal work of the first three authors was upon Vanessa and 
Pyrameis. Van Bemmelen ('89) has shown that the first color to appear in 
Pyrameis cardui is a pale brownish yellow which deepens to the reddish brown 
ground color; upon this ground color, the black spots appear. The development 
of the color in Vanessa urtice follows very much the same sequence, as pointed 
out by both Van Bemmelen and Urech. | Urech (91) has shown that in Vanessa 
io, the adult spots and colors appear directly upon the primitive white of the 
pupal wing; that is, the yellow appears over a restricted area of the wing; 
following this, a reddish tinge appears, which, over another portion of the wing, 
gradually deepens to the reddish brown ground color. Later, the adult black 
spots develop directly upon the primitive white wing; some at least of the white 
spots of the adult represent the primitive white of the pupal wing. In Van 
Bemmelen's opinion, a considerable amount of modification takes place in the 
wings after the first appearance of color, so that the adult design may differ 
considerably from that first laid down. Urech’s (791) view is directly opposed 
to this; according to him, the different color areas are definitely laid down from 
the beginning and are therefore older phylogenetically than the particular colors 
of the adult wing. Не therefore regards color as the important factor in deter- 
mining phylogenetic position—‘‘die Farbe ist das Primäre, die Zeichnung das 
Secundiire.”’ 
Haase (93) worked upon several species of Papilio and found that the 
wings are transparent or colorless, later becoming whitish; this white then gives 
way to a yellowish ground color upon which the adult colors begin to appear, 
undergoing considerable development before reaching their definitive adult 
condition. 
Mayer (’96) traces the development of the scales from modified hypodermis 
cells, the “formative cells of the scales,” from their first appearance as blunt 
outgrowths from these cells until they are fully formed and pigmented. In 
addition to confirming the conclusions of previous investigators as to the sequence 
in the appearance of colors, Mayer has shown that “the transparent condition 
of the wings corresponds to the period before the scales are formed and to the 
time when they are still completely full of protoplasm. The white condition is 
caused by the withdrawal of the protoplasm from the scales, leaving them as 
little hollow bags filled with air. In this condition, they diffract the light and 
appear pure white. 
“After the protoplasm has completely withdrawn from the scales, the 
