396 



playing joyously at intervals with each other ; or, gaily perched, 

 sip nectar from their favourite flowers. " * What keeps such insects 

 from wandering 1 



Mr. Bates, iu reference to the limited ranges of closely allied 

 species of buttei-fly in the plains of tropical America, remarks that 

 the most efiective possible barriers are sometimes opposed to the 

 spread of species " without any physical barrier existing which is 

 perceptible by our senses." And he believes the explanation of the 

 fact to be — " That there really are subtle differences of physical 

 conditions from place to place, even in a uniform region ; slight 

 differences in soil, humidity, succulence of foliage, and so forth, 

 which require in each a readjustment of the constitution of any 

 new immigrants from adjoining areas ; but that each area being 

 kept well stocked with allied species already adjusted to its minute 

 conditions, such migration rarely occurs." t 



This reasoning would probably be found to apply to numerous 

 cases in our own country, in which we find closely allied species in- 

 habiting contiguous areas of greater or less extent without inter- 

 mixing ; and it is suggestive of many points of inquiry to be made 

 by the local entomologist in connection with the circumstance. 

 Perhaps in the case of the Papilio cinxia, alluded to above, 

 we may suppose that, being naturally slow fliers, and meeting 

 with all they require in a particular spot, they have no inducement 

 to leave it, unless their numbers so increase as to oblige them to 

 do so. 



There are other remarkable cases in which species met with 

 generally on the coast, and from which they seldom if ever wander, 

 are found to occur in places far inland. Thus it is recorded by 

 Mr. Barrett, an entomologist in the eastern counties, that at 

 Brandon, in Suffolk, he finds several species of Lepidoptera, some 

 in abundance, which have always been considered as " most exclu- 

 sively coast sand-hill insects;" the soil of Brandon being "a loose 

 light sand, precisely such as is found on the North Denes, at 

 Yarmouth, at the present time." His explanation of the phe- 

 nomenon, on the authority of an eminent geologist, is " that this 



* Lepidoptera Britannica, p. 149. 

 t Ent. Trans, 1869. Proceed., p. xlvi. 



