WALKING-STICKS AND WALKING-LEAVES 77 



may be remarked, that not only is it less rich in Phasmidae 

 than the Oriental hemisphere, but the species there have 

 a tendency more pronounced to remain apterous. 

 Among what may be called wingless species of the 

 Orient, more usually the rudiments of wings are apparent, 

 or the wings are more or less developed, although of 

 the briefest description. From these differences, and 

 others, it follows that the genera of the different conti- 

 nents are in great part distinct. Not only is this the 

 case, but the greater number of species are confined 

 within somewhat narrow geographical limits. It is easy 

 to understand how insects so little addicted even to 

 walking do not spread rapidly, and that, seeing their 

 absolute dependence on plants which serve at once as 

 their abode and their nutriment, they are affected more 

 strongly than others by the modifying influence of the 

 places which they inhabit ; whence it comes that each 

 little region possesses its species. 



Existence is possible to the Phasmidae only in verdant 

 regions, where delicate nourishment is always to be had 

 within reach. They could not live in a dry climate, and 

 on a soil often deprived of vegetation, their limited 

 powers of locomotion being an insurmountable obstacle 

 to their travelling over great distances in search of food. 

 These facts explain at once the rarity of phasmidae in 

 tropical Africa, and the manner in which they pre- 

 eminently affect the humid and verdant isles of the 



