LETTER OF DECEMBER 12TH, 1857. 13 



stood as announcing positively, or as the final inductions to 

 be drawn from my studies. These are : 



1. That in any given species, the pterogostic characters 

 of the wings are invariably identical in all individuals of 

 that species. 



2. That modifications in the neuration of the posterior 

 wings, which involve a change of type, constantly carry with 

 them physical changes and differences in habits, recognized 

 as family distin ctions. 



3. That variations from any given type in the neuration 

 of the anterior wings in the same families, or those in which 

 the neuration of the posterior wings is similar, indicate the 

 existence of minor physical modifications and differences in 

 habits, necessary to constitute generic relationships. 



The latter proposition stands on the least positive basis, 

 but I trust I shall be able to demonstrate the correctness of 

 all at some future time ; provided I do not hereafter ascertain 

 I have generalized hastily and unphilosophically. For this 

 purpose I am extending, as industriously as I am able, the 

 data from which they are deduced. This, at best, is slowly 

 and laboriously, and I do not conceal from myself that there 

 exist many difficulties and perplexing problems, which even 

 the cleverness of Guenee has not clearly elucidated. If neu- 

 ration has any real value as a " dominator * character," indi- 

 cating natural affinities, its verification will not be the work 

 of one student, nor one pair of hands, but of many industrious 

 painstaking workers. 



Permit me, therefore, to hope your judgment will approve 

 a suggestion I will take the liberty of making, as one much 

 interested in the usefulness of your " Natural History of the 

 Tineina" to the entomological student. This is, that the neu- 

 ration of each member of a genus be given in the work, in 

 order that all the modifications, if there be any, may be 

 shown. I think this would increase its cost but little, if any, 

 and I am sure would be regarded by every systematist as a 



* See note in the preceding page. 



