72 THE NATURAL HISTORY 



locustella, hinted at by Dr. Derham in Ray's Letters : see 

 p. 108. He also procured me a grasshopper-lark. 



The question that you put with regard to those genera 

 of animals that are peculiar to America, viz. how they 

 came there, and whence ? is too puzzling for me to 

 answer ; and yet so obvious as often to have struck me 

 with wonder. If one looks into the writers on that 

 subject little satisfaction is to be found. Ingenious men 

 will readily advance plausible arguments to support 

 whatever theory they shall choose to maintain ; but then 

 the misfortune is, every one's hypothesis is each as good 

 as another's, since they are all founded on conjecture. 

 The late writers of this sort, in whom may be seen all 

 the arguments of those that have gone before, as I 

 remember, stock America from the western coast of 

 Africa and the south of Europe ; and then break down 

 the Isthmus that bridged over the Atlantic. But this 

 is making use of a violent piece of machinery : it is a 

 difficulty worthy of the interposition of a god 1 " In- 

 credulus odi." 



THE NATURALIST'S SUMMER-EVENING 

 WALK 



. . . cquiileni credo, quia sit divinitus illis 

 Ingeuium. Virg. Georgics. 



When day declining sheds a milder gleam. 

 What time the may-fly * haunts the pool or stream ; 

 When the still owl skims round the grassy mead. 

 What time the timorous hare limps forth to feed ; 



* The angler's may-fly, the ephemera vulgala Linn., comes forth 

 from its aurelia state, and emerges out of the water about six in 

 the evening, and dies about eleven at night, determining the date of 

 its fly state in about five or six hours. They usually begin to appear 

 about the 4th of June, and continue in succession for near a fort- 

 night. See Swammerdam, Derham, Scopoh, etc. 



