122 APPLE AND WALNUT LEAF-CKDMPLEE8. 



between the nursery row8» from which the insects had been pecked 

 by these birds. Mr. "Whitney further remarked that he had noticed 

 that a considerable fall of enow would give the quails a vantage ground 

 which enabled them to obtain those worms which were, ordinarily, 

 above their reach. 



With respect to the parasites of the P. juglandis^ I may here state 

 that I have bred from their cones two distinct species of Ichneumon- 

 fly, one of which was different from the species obtained from the 

 Fhycita nebula. 



THE QUESTION OF SPECIEIO IDENTITY. 



"Whether the insects here described (and the question applies equally 

 to many other similar cases), be distinct species, or only plant varieties 

 of the same, is at present merely a matter of conjecture, or of personal 

 opinion. The question could be definitely settled only by a series of ex- 

 periments, extending through a long period of time, in which the insects 

 should be changed from one kind of plant-food to the other, and notice 

 taken whether there were a gradual tendency to those variations which 

 we now see to exist. 



The whole subject of the variation of species according to difference 

 of location, food, and other circumstances, is one which is attracting 

 much attention amongst naturalists at the present day. It involves the 

 important question whether there really be in nature any such thing as 

 species, in the ordinary acceptation of that term ; that is, whether there 

 be any definite and permanent forms which have existed in the indefi- 

 nite past, subject, as a general rule, only to slight variation, and always 

 tending to return to the original and normal type ; or whether what we 

 call species are only varieties of a comparatively more permanent form, 

 and this permanency owing simply to the force of circumstances, and 

 not to any inherent law of their being. 



The subject is also of interest as having an important bearing upon 

 what has been heretofore known as the development theory, but which 

 is at present more commonly called the Darwinian theory, after the 

 name of its most able and popular expouader. Every well-attested 

 fact which shows the gradual and constant change of organized forms, 

 tends to open the way for a more general reception of this theory, by 

 showing that our pre-conceived notions of the original creation of spe- 

 cies, essentially in the forms in which they now exist, cannot be main- 

 tained. But this is not the place to discuss these profound and difBcult 

 questions in the philosophy of natural history. It has been our object 



