EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 121 



ment ontogenetique, sont analogues aux phases que le dessin de Tespece du 

 Papillon a dti parcourir pendant son developpement phylogenetique, que le loi 

 qui gouverne la biogenese est aussi confirmee par ce procede, qui s'accomplit 

 pendant la metamorphose de Tinsecte^ et qu'en fin les theories de Eimer sont 

 solidement fondees, quand il dit que chaque animal ne pent varier que dans peu 

 de directions determinees par les influences du dehors et par sa propre consti- 

 tution, et que Fespece se forme par genepistase/^ 



Recapitulation is, however, only partial and confined to primitive forms: 

 ^^Les phenomenes de la phylogenese se produisent le plus clairement dans 

 le developpement du dessin chez les formes les plus primitives. Chez les groupes 

 les plus advances, ces phenomenes sont masques par ^intervention dela tachy- 

 genese qui montre sa plus grande influence dans le developpement des ailes 

 inferieures.'' 



With regard to the succession of colors upon the wing, the same author 

 finds that it is only in the primitive forms that the scales forming the dark mark- 

 ings pass through the intermediate shades of yellow to reach their final gray or 

 black condition; in the higher forms, they remain uncolored until the scales 

 forming the ground color reach their full development, later passing directly 

 from the colorless stage into gray or black. The color appears first at the tip 

 of the scales, spreading gradually to the base. Scales which are destined to 

 acquire their pigment later are not fully formed when the scales of the ground 

 color attain the adult form and color. Therefore, color may be taken as a 

 measure of the degree of development of a scale. 



2. Methods. 



In the study of the development of color in the wings of Lithocolletis , speci- 

 mens of the summer generations were used for observation. No overwintering 

 pupse have been observed. In the summer generations, the average duration 

 of the pupal state is about a week; it may be as short as four or five days. 



The chrysalids were removed from the mines shortly after pupation and 

 kept under careful observation. For some time, no change in the brown color 

 of the pupa is to be observed, then two faintly darker brown spots, corresponding 

 in position with the eyes of the imago, become visible through the pupal envelope. 

 These spots rapidly turn black, and very shortly after, the wings, which up to 

 this time have appeared transparent through their thin chitinous envelope, 

 begin to lose their transparency. This marks the beginning of the white stage. 

 A day or two later, the yellow colors begin to appear upon the wing. The chief 

 difficulty in the study lies in securing a suitable series of these earliest stages, 

 as the colors are very faint at this period, and numerous dissections are often 

 required before the necessary material can be obtained. In later stages, the 

 markings are visible through the pupal envelope, and a choice of specimens can 

 be made with relative accuracy. 



The dissections were made in .6 per cent NaCl solution under a simple 



