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 Schaffer (^89), Van Bemmelen 

 ('89), Urech ('91), Haase ('93), Mayer ('96) 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 cardid 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 urticce follows very much the same sequence, as pointed 

 out by both Van Bemmelen and Urech. Urech ('91) has shown that in Vanessa 

 10, 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 ('91) 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. He therefore regards color as the important factor in deter- 

 mining phylogenetic position— ''die Farbe ist das Primare, die Zeichnung das 

 Secundare." 



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 cehs 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 fuh 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 



