ANIMALS— PHYSICAL ENVIRONMENT 113 



proportions ; in others they are present as minute 

 vestiges, or so reduced that their sole function is to 

 assist in the production of the insect's chirrup. 

 In some species the reduction has proceeded much 

 further in one sex than in the other. Short-winged 

 forms may be observed in the Long-horned and 

 Short-horned Grasshoppers, in the Mantis family, 

 and in the Crickets, so that they must have arisen 

 independently many times in the Orthoptera. The 

 phenomenon is not by any means confined to desert 

 species, but is much more frequently seen in them 

 than in those of other environments. For instance, 

 in Algeria and Tunisia about half the Orthoptera 

 are wingless, even when the forms which inhabit the 

 fertile coastal region are included in the count. 



Among the Coleoptera (Beetles) fusion of the 

 wing-cases and consequent flightlessness is a char- 

 acter of very many Tenebrionidse (Fig. 42, facing p. 

 150) and Carabidae (Ground Beetles) in deserts. Loss 

 of the power of flight in these two families of beetles 

 and in the Orthoptera is not confined to species 

 which inhabit deserts, but is much more common 

 among them than among others. That it is due 

 solely to the wind and not to any other infiuence is 

 apparent from the fact that a similar loss of the power 

 of flight occurs in many other environments which 

 are exposed to violent winds, but do not in any 

 other respect resemble deserts : the insects of 

 mountain tops and of small isolated islands furnish 

 examples. 



The dispersive effect of the wind upon small 

 animals can be exercised in the absence of any modi- 



