FURTHER RESEARCHES ON NORTH AMERICAN ACRIDIID^. 9 



The coloration of each of these surfaces needs to be studied in 

 correlation with that of the others and with direct observations on the 

 habits and distribution of the insects in the field. That of the first 

 class of surfaces has received scant attention, much less than it 

 deserves. It is probably chiefly physiological in character. That of 

 the second class is, with few exceptions, highly sympathetic, harmo- 

 nizing or resembling very closely, often to a marvelous degree, the 

 background of the creature's environment. Earth tints, rock and 

 sand textures, the infinitely varied browns, greens, and grays of living 

 and dead vegetation, yellow, orange, rose, and silvery white are all 

 represented, in spots and streaks, the effect being to merge the insect 

 indistinguishably in its background while at rest, thus shielding it in 

 a very high degree from the observation of its foes. These colors are 

 of very great protective value at the present time, natural selection 

 continually acting to preserve and perfect them, but, though highly 

 protective in character, they are without doubt primarily due to 

 physiological processes and influences as yet imperfectly understood. 



The colors of the third class of surfaces are, on the contrary, in 

 many cases non-sympathetic in character to a high degree; they are 

 often bright and strongly contrasted, striking in effect and at times 

 exceedingly conspicuous. This is very generally the case among the 

 North American Oedipodinse and certain Acridiinae. What is the 

 function, the significance of these colors, in these places, seen only in 

 flight or when especially displayed? Let us consider the color of the 

 wings first. 



Vessel er, in his most important work (Zool. Jahrb., Abh. f. 

 Syst., Bd. 16, 17), misled by the natural-selection theory, tries mis- 

 takenly to apply it to this kind of wing-coloration, assigning to these 

 colors a protective value through "contrast-mimicry" by a dazzling 

 of the pursuer through their sudden appearance and disappearance. 

 As a matter of fact, in American species at least, these colors are 

 usually exposed continuously during flight. 



This explanation is a needless tax upon the imagination. There 

 is a much simpler one which is almost forced upon the attention of 

 the stroller in the fields, and which may be readily observed by taking 

 a favorable position in a station thickly populated with adult Trimero- 

 tropis, Arphia, Spharagemon, Hippisctis, Dissosteira, or other similarly 

 decorated Oedipodinae. 



The flight of one of these locusts attracts attention by its crepi- 

 tating character; the conspicuous wing-colors, red or yellow and 

 black, in strong contrast, render its flight easy to follow, as it is very 

 frequently followed, by others, which drop to the ground in close 



