99 



is everywhere inclined (if at all) to be especially stimu- 

 lated : whilst, as regards the second, it will be sufficient 

 to state, that in continents, when any decided alteration 

 takes place in the organs of flight, it for the most part 

 comes to pass that an increased (rather than diminished) 

 action is the result ; whereas in islands, provided that 

 the species are not absolutely dependent on aerial pro- 

 gression for their food (in which case, in order to 

 prepare for the contingency of being blown out to sea, 

 the capacity of the wings is commonly augmented), the 

 reverse is nearer the truth. So that the second problem, 

 the reason why appendages thus apparently essential 

 should be subject to inconstancy, is at once rendered 

 intelligible from the consideration, that it is only under 

 circumstances in which the indiscriminate employment 

 of those organs would be apt to bring the creatures into 

 trouble that (when not an actual sine qua non to their 

 existence) they are liable to be taken away ; whilst, even 

 in that case, it generally happens that some partial equi- 

 valent for the privation incurred is granted, as a recom- 

 pense. 



Mr. Westwood, in his admirable Introduction to the 

 Modern Classification of Insects, has recorded many 

 instances of alary variation ; which, however, as he does 

 not appear to have noticed the peculiarity of island 

 faunas, are principally in corroboration of what I have 

 just insisted upon as the usual tendency in continents, 

 namely, an enlargement of the erratic powers. Speak- 

 ing of the Aphelocheirus cestivalis (a member of the 



