Sends his paper on "Willow-galls" [Proc. Entomol. Soc. Philadelphia 3 (1864): 543–644].
Lengthy criticism of Agassiz’s views on species as stated in his Essay on classification [1857].
Interested by CD’s trimorphism in Lythrum. Thinks some great mystery may lie in the fact that in some genera, some species are tri-, some di-, and some monomorphic, and in other genera, Apis, Vespa, Bombus, all the known species are dimorphic.