I think I’ve mentioned before that I keep a copy of Burkhardt’s Selected Letters of Charles Darwin handy in the smallest room (“for fun“). In this letter to Asa Gray in November 1857, a load is lifted from Chaz’s mind…
By the way I must tell you what I heard yesterday, though not in your line, but on subject of the crossing of individuals. Barnacles (Balanus) are hermaphrodite & with their well shut up shell offer as great a difficulty to crossing as can well be conceived: I found an individual with a monstrous & imperforate penis, but yet with fertilised ova; but I did not know whether it might not be case of parthogenesis or a strange accident of some floating spermatozoa. Well yesterday I had an account by a man who, watching some shells, saw one protrude its long probosciformed penis, & insert it in the shell of an adjoining individual! So here is a load off my mind.