Thanks TTTT for his study of European spiders [On European spiders Part 1 (1869–70)] which bases its classification system on the theory of evolution.
Down. | Beckenham | Kent. S.E.
20 April 1870
[Darwin expresses heartfelt thanks to Tord Tamerlan Teodore Thorell, a juniorprofessor of zoology at the University of Upsala, Sweden, for a copy of his OnEuropean Spiders.]f1
I have looked through it & have admired the wonderful research &labour which you have bestowed on this highly useful work. It has been a greatsatisfaction to me to observe in one or two passages, especially in anadmirable discussion on the principles of classification, that you believe inthe evolution of speciesf2