Grateful for AH’s long letter and suggestions. Delighted at what he says about "complemental males". CD feared no one would believe in them but now that Owen, Dana, and AH accept them, he is content.
Agrees with AH on cross-impregnation; has collected facts on this head but has done nothing with them.
AH’s paper on Alcippe [Ann. & Mag. Nat. Hist. 2d ser. 4 (1849): 305–14] caused him to lose sleep over its anomalous structure.