EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 163 



spots which are situated near the edge of the wing is largely controlled by the 

 wing-folds or creases." 



Eimer has derived the various types of coloration from a series of transverse 

 stripes (termed by him longitudinal because parallel to the longitudinal axis 

 of the body) which break up into spots which fuse crosswise to form markings 

 parallel to the longitudinal nervures, and finahy fuse to a uniform color. New 

 markings appear on the body of the animal from behind forwards and from above 

 downwards, or conversely, whilst the old ones disappear in the same direction 

 and succession. 



I have shown that the ground color has been derived from a series of such 

 transverse elements; conversion into a uniform color has taken place directly 

 by an extension of color onto previously unpigmented areas, distad through the 

 middle of the wing in the ceh, proximad on the margins. The positions of the 

 markings are arbitrarily determined. They are dependent upon the level at 

 which evolution in the pattern of the ground color acting in a few definite direc- 

 tions has come to a standstill. The actual appearance of the markings is prob- 

 ably due to physiological activities whose nature is not understood. The first 

 markings are usually transverse, rarely longitudinal when the modification 

 in the ground color has been far-reaching. These transverse markings are in 

 the nature of narrow lines or streaks, phylogenetically the forerunners of the 

 bands of higher Lepidoptera. Since the streaks and lines of dark scales in Litho- 

 colletis still retain their primitive condition as originally laid down, it is not to he 

 expected that the laws which Mayer has given, based upon the transformation of 

 spots and bands in the higher Lepidoptera, would find wide application in this 

 group. Portions of a pair of such streaks in Lithocolletis will be found at the 

 margins and in each interspace which the band from which they are derived 

 crosses. Breaking up of bands formed by the growing together of these streaks 

 will result in conditions such as Mayer has described for spots and series of spots. 

 Any spot such as the apical spot is bilaterally symmetrical and occupies the 

 center of its interspace. The primitive bands from which the ground color has 

 been derived and which have been regarded as a primary set of markings upon 

 which a second set, the markings proper, have been superimposed, have exhibited 

 the tendency toward shrinking away at each end. 



The ultimate causes which determine the definitive positions of the primitive 

 bands are unknown. Von Linden has found that in the lower orders of insects, 

 the coloring matter has a tendency to collect on transverse veins; this however 

 does not bring us any nearer to a real explanation of the phenomenon of colora- 

 tion. The probability that the origin of the markings, which appear secondarily, 

 may be traced directly to physiological factors, renders it reasonable that the 

 appearance of the primary series is conditioned by like physiological and morpho- 

 logical factors within the organism itself and is independent of external factors. 



Evolution in the pattern of the primitive series of bands has been shown to 

 have taken place in a few definite directions; the diverse patterns which have 



