1874.] ANTS. 369 



C. Darwin to Aug. For el. 



Down, October 15, 1874. 



My dear Sir, — I have now read the whole of your admir- 

 able work * and seldom in my life have I been more inter- 

 ested by any book. There are so many interesting facts and 

 discussions, that I hardly know which to specify ; but I think, 

 firstly, the newest points to me have been about the size of 

 the brain in the three sexes, together with your suggestion 

 that increase of mind power may have led to the sterility of 

 the workers. Secondly about the battles of the ants, and 

 your curious account of the enraged ants being held by their 

 comrades until they calmed down. Thirdly, the evidence of 

 ants of the same community being the offspring of brothers 

 and sisters. You admit, I think, that new communities will 

 often be the product of a cross between not-related ants. 

 Fritz Miiller has made some interesting observations on this 

 head with respect to Termites. The case of Anergates is 

 most perplexing in many ways, but I have such faith in the 

 law of occasional crossing that I believe an explanation will 

 hereafter be found, such as the dimorphism of either sex and 

 the occasional production of winged males. I see that you 

 are puzzled how ants of the same community recognize each 

 other; I once placed two (^F. rufa) in a pill-box smelling 

 strongly of asafoetida and after a day returned them to their 

 homes ; they were threatened, but at last recognized. I made 

 the trial thinking that they might know each other by their 

 odour ; but this cannot have been the case, and I have often 

 fancied that they must have some common signal. Your 

 last chapter is one great mass of wonderful facts and sugges- 

 tions, and the whole profoundly interesting. I have seldom 

 been more gratified than by [your] honourable mention of my 

 work. 



I should like to tell you one little observation which I 

 made with care many years ago ; I saw ants {Formica rufa) 



* ' Les Fourmis de la Suisse,' 4to, 1874. 



