HIPPODAMIA. 



37 





MODIFICATION. 



Subjection of the prepupa and pupa to an ordinary poultry incubator at 

 40 C. resulted in no appreciable modification, nor did increase or decrease 

 in humidity. But an increase of 

 pigment was obtained by expos- 

 ing the prepupa and pupa to the 

 cold of a refrigerator (5 to 15 

 C.), a cellar (15 to 17 C.), and 

 the intermittent temperature of 

 an ordinary room where the 

 temperature dropped during the 

 winter months from 12 to 18 C. 

 by day to 5 C. at night. The 

 greatest degree of pigmentation 

 resulted in the last case. The 

 result from one experiment, in 

 which the prepupae of typical 

 Hippoda m ia con vergens were 

 subjected to a freezing tempera- 

 ture out of doors for two nights, 

 was the elytral pattern shown in 

 fig. 25, which is much like that of 

 the western mountain beetles. 

 The other cases give the prono- 

 tum that is so frequently found 

 in the western beetles, but elytra 

 not corresponding to any known 

 variety. Fig. 26 is a composite 

 drawing, no one beetle showing i 

 the same high degree of pigmen- 

 tation at every point. Some fea- ( 

 tures of this modification pattern 

 show a correspondence to some 

 of the varieties in nature ; other features are produced only by artificial 

 modification, especially the pigment line between 1 and 4, which is not 

 the same as the vitta in Hippodamia spuria var. or H. apicalis var. 



HEREDITY. 



Every variety or noticeable variation which has been tested is inher- 

 itable in some degree. Even though the variety has been brought from a 

 different region, it has maintained itself in our vivarium. 



The heredity of spot 1 + 3 shows a nearly perfect segregation. There 

 is a lower degree of segregation in the confluence of 4 and 5. The closest 

 approach to blended inheritance is in the size of the pronotal dash and the 

 incomplete lateral margin of the pronotum. Yet in each of these cases it 



FIG. 23. Variation of the diameter of spot 2 in Hippo- 

 damia convergent at Fairfleld, Washington. 



