26 MY LIFE [Chap. 



velocity, I think you will find that the difference of re- 

 sistance is nothing like commensurate with the difference 

 of size between the muscles that raise the wings and the 

 muscles that depress them." The reason of this great 

 difference could not be accurately explained at that time, 

 but a few years later, Marey, by his ingenious experiments 

 and photographs, showed that while the whole upward 

 motion of the wing is very gradual, the downward stroke, 

 though equally gradual at the beginning and the end, is two 

 or three times as rapid in the middle, thus giving the great 

 upward and onward impulse, necessitating the extremely 

 large muscles noted by Spencer. An excellent short account 

 of the whole mechanism of the flight of birds, with many of 

 Marey's diagrams and illustrations, is given in Professor 

 A. Newton's " Dictionary of Birds," in the article " Flight," 

 and is the clearest exposition of the subject I have yet seen. 



In 1872, in my presidential address to the Entomological 

 Society, I endeavoured to expound Herbert Spencer's theory 

 of the origin of insects, on the view that they are funda- 

 mentally compound animals, each segment representing one 

 of the original independent organisms. This theory is ex- 

 pounded at some length in the second volume of his 

 " Principles of Biology " (chapter iv., " The Morphological 

 Composition of Animals "), but had apparently been almost 

 unnoticed by English entomologists. On sending him a 

 copy of the address, he wrote to me as follows : " It is 

 gratifying to me to find that your extended knowledge 

 does not lead you to scepticism respecting the speculation 

 of mine which you quote, but rather enables you to cite 

 further facts in justification of it. Possibly your exposition 

 will lead some of those, in whose lines of investigation the 

 question lies, to give deliberate attention to it." 



This communication gave me much pleasure, because the 

 subject was one quite out of my own domain, and though I 

 had taken a good deal of trouble to understand his views and 

 to represent them accurately, and had also adduced a few 

 additional facts in support of it, yet the subject was so novel 

 and so complex that I was rather afraid I might have made 



