Dichromatis7n in Lina Lapponica. 119 



having a median dorsal area of black covering one-half of the 

 dorsal surface, and marginal areas that are white when the insect 

 first emerges, and turn a copper-red about six days later. A 

 single black spot is present w^ithin each marginal area. 



For the purposes of this year's study no account was taken of 

 the variation within each series, namely, the fluctuating variations, 

 and their behavior in heredity, as this demands a special series of 

 experiments. 



I began the present series of experiments with the notion that 

 the melanic variety was the possible result of a coalescence of all 

 the spots in the spotted variety. A study of the color develop- 

 ment at ecdysis, however, revealed the fact that the dark pigment 

 giving the melanic series its color is superimposed on the spotted 

 condition. The wing covers of an adult that has just slipped out 

 of its pupal case are at first white (PI. i. Fig. i). Within a few 

 minutes the spotted areas, first the anterior, then the middle, and 

 lastly the posterior are dimly but distinctly indicated as light drab 

 color against the white background (PI. i. Fig. 2). The spots 

 deepen gradually to a dark drab, and the ground color becomes a 

 light drab (PI. i. Fig. 3). In the melanic series these two steps, 

 namely, pigmentation of the spotted areas and pigmentation of the 

 rest of the wing cover, occasionally take place almost simultane- 

 ously, the spotted areas then becoming so obscured as not to be 

 apparent. Their presence in every doubtful case, however, was 

 determined by holding the wing cover between the light and the 

 observer. From the drab stage development proceeds in one of 

 two directions. In one series of individuals, including both males 

 and females the spots deepen to black, and following quickly upon 

 this change, the drab ground color gives way to brown pigment 

 against which the fourteen black spots are clearly marked (PI. i. 

 Fig. 4). In the other series, the spots as before deepen to black, 

 and the drab gives way to black pigment (PI. i, Fig. 5). This 

 soon overshadows and totally obscures the spots from surface 

 view (PI. I, Fig. 6). Their presence may still be demonstrated, 

 however, by holding the wing to the light. 



It appears, therefore, that in Lina lapponica we have to deal 

 in its dichromatism with a case of "substantive discontinuous^ 

 variation." Each individual is either melanic, B, or not melanic, 

 S, all individuals alike being spotted. 



*Bateson; "Materials for the Study of Variation." 



