570 [December 



There is a very prevalent idea in the Agricultural community, that 

 all that is required, in order to devise remedies for the depredations of 

 any given Noxious Insect, is to investigate the Natural History of that 

 one given Insect. The cases of the Hessian Fly and the Wheat Midge 

 — two insects which annually damage the people of the United States 

 to the extent of ut least a hundred million dollars — prove, I think, sat- 

 isfactorily, that it is impossible completely to unravel the intricacies of 

 the Natural History of certain Noxious Insects, unless we first become 

 well ac(}uainted with the Natural History of their congeners. As well 

 might we attempt to delineate the path of a Comet, without first becom- 

 ing acquainted with the laws that regulate and control the whole Solar 

 System. Without such collateral knowledge, we shall sometimes — in- 

 stead of recognizing that Unity of Habits in every genus, which is 

 the very essence of the thing that we call a Grenus, because Habits are cor- 

 related with Structure, and Structure makes the Genus — become prone 

 to believe in the existence of several fundamentally different and hete- 

 rogeneous habits in one and the same genus, we shall be liable to accept 

 as indisputably true the most absurd and contradictory and anomalous 

 statements from others, and we shall ourselves be led into errors and 

 hallucinations without number, and in these minute objects be occa- 

 sionally deceived by optical illusions and phenomena which exist only 

 in the imagination. 



" The observer," says O-sten Sacken, " must see well and render only 

 u-hnt he has seen ; a condition much more difficult to comply with, in 

 matters of Natural History especially, than is usually imagined." 

 {Proc. Enf. Soc. Phi/. I. p. 47.) " It is well," says the English cou- 

 chologist. Dr. P. P. Carpenter, '' in the present state of science, to take 

 NOTHING ON TRUST. What is copied from book to book, and what is 

 repeated from figure to figure, may be correct; but then on the other 

 hand it may not. * * It is curious how large a proportion of existing 

 observations on Mollusks need verification by those who have honest, 

 well-trained eyes. Just as the infant's eye has to be trained to distin- 

 guish forms and distances, so it requires practice, before we know how 

 to see truly an object that lies before us. During the educational pro- 

 cess, it is often very easy to see what we loish or expect to see." {^Rep. 

 Smithson. Inst. 1860, pp. 280, 231.) If, then, error is as rife in Sci- 

 ence as the above observations would lead us to suppose, surely the 



