LETTEK OF JUNE 23KD, 1860. 33 



from a struggle for existence adds nothing to our knowledge, 

 and is flatly contradicted by all our physiological facts. It is 

 really a revival of the doctrine of Yon Bar enunciated nearly 

 fifty years ago, " That heterogeneous or special structure 

 arises out of one more homogeneous or general, and this by 

 means of gradual change" This united to the doctrine of 

 transmutation puts us in possession of the entire Darwinian 

 theory. 



Prof. Agassiz is now writing a reply to his argument, and 

 in this, all that can be urged in favour of immutability will 

 be ably advocated and represented. Even if the theory of 

 the immutability of species must be abandoned, from the 

 accumulation of testimony against it, there is still, in my own 

 view, a safe and reasonable intermediate position which can 

 be occupied. This I conceive is indicated in the proposition 

 of Dr. Le Conte as contained in my introductory remarks in 

 the Synopsis of the N. A. Sphingidce. 



I have been preparing to write a Monograph of the Ameri- 

 can Tineina, but greatly to my regret I must defer the com- 

 mencement of the work for at least another year. All the 

 material that is accumulated results from my own industry, 

 and thus far my captures have been almost purely local. 

 At the end of this season I shall be able to determine how 

 much and what kind of assistance I shall receive from others. 

 A few students and collectors are collecting for me at present 

 in various parts of the country, but the region thus occupied 

 is not by any means sufficiently extensive. They are all 

 north of 38 N. latitude, and all my efforts are now devoted 

 to obtaining collections south of this, or in the extreme 

 southern states, but thus far without any success. 



It may interest you to know that I have constructed a 

 Synoptical Table of all the British Genera of the Tineina, 

 including those groups which I have described as new ones, 

 and carried it out rigidly on the basis of structural characters. 

 I have done this chiefly for my own convenience, but with 

 the intention likewise of using it in a monograph of our own 



