8 FURTHER RESEARCHES ON NORTH AMERICAN 



erly summer winds ; frequent tornadoes (northeast), and debris-bearing 

 river floods (east and southeast). Dispersal being thus amply pro- 

 vided for, colonization or permanent extension of range is dependent 

 on the conditions (chiefly chemical and physical) affecting the phys- 

 iological welfare of the accidental or intentional migrant.* 



Brachypterous species are much less numerous proportionally in 

 the treeless arid districts than in humid, forested regions, East or 

 West. When present, they inhabit shrubby or herbaceous thickets. 

 It is a noteworthy fact that (excluding the aberrant group Tettiginse) 

 every flightless species of locust known from the eastern half of the 

 continent is phytophilous, as distinguished from geophilous, in habits. 



LOCUST COLORATION. 



In consideration of certain misapprehensions as to the biological 

 significance of the colors borne by the Acridiidae, a few general state- 

 ments regarding the coloration of these insects will not be amiss. 



The Acridiidae exhibit both structural and pigmentary colors. 

 An example of structural color is the iridescence of the wing mem- 

 branes, shown especially well in the Tettiginae, some Melanopli, and 

 other species with transparent wings. All the other colors are pig- 

 mentary in character, at least in part, and doubtless originate in the 

 life-processes of the body. Those of sympathetic character i. e., 

 resembling the environment are in many cases, e. g., among desert 

 species, perhaps originally physiologically protective in function, as 

 suggested by Gadow for reptiles ; the exposed non-sympathetic colors 

 probably possess a biological significance varying with the position 

 and use of the organs on which they are displayed. 



A locust presents three classes of surface with reference to colora- 

 tion: ist, the ventral part of the body next its supporting surface 

 earth or plant which is shielded to a great extent from external 

 influences such as the action of light, etc., and the observation of 

 birds and other enemies; 2d, those parts continually exposed, day 

 and night, at rest and in action, to the influences above-mentioned, 

 comprising the dorsal, lateral, anterior and posterior surfaces; 3d, 

 those parts exposed only occasionally, and usually for brief periods 

 only, during attack, courtship, or other exciting circumstances, or 

 while in rapid motion, comprising the wings, hind tibiae, inner and 

 under sides of hind femora, and sides of base of abdomen. 



*The presence or absence of a given species in a locality is largely depen- 

 dent on the character of the habitats represented. If woodland is lacking, sylvan 

 species are absent; if ledges or similar rock surfaces are not at hand, saxicolous 

 species will not be found. 



