My dear M^r Darwin,

I need hardly say that I felt highly delighted to get your very kind note of last September.¹ I fully endorse what you say of M^r. Meehan.² His trouble is that he has not been so trained that he can appreciate a truth whether it conflict with his own opinions or not. There is a bias in most everything he writes or says, and he is especially fond of controverting generally-accepted doctrine, upon his own observations—oft-times insufficient and even inaccurate. He is, withal, unfair, not to say untruthful. I had a good illustration of this fact at Cincinnati last August. During the Summer, at his invitation, I spent a day and evening at his nursery at Germantown Pa purposely to show him the working of Prodoxus, as distinguished from Pronuba.³ I went just as Yucca angustifolia was losing its last top flowers and Y. filamentosa was about to open its first flowers.⁴ Meehan has whole beds of this last and his place furnishes unusual facilities for correct observation.

The old, last year’s stems of filamentosa were riddled with the holes of exit which Prodoxus decipiens had made and the moths had been busy ovipositing in the green stems. These were, withal, so numerous that they flew everywhere, toward evening, about the place, and during the day crowded in the few remaining flowers of angustifolia, though not a fruit set on that species except where Meehan himself had artificially pollinized. I collected over fifty moths from a single flower, and brought home in all several hundred. I showed him that there was not a single Pronuba among them and upon meeting him again at Cincinnati informed him that a more careful examination of the many I had brought home proved them every one to be Prodoxus decipiens. He read a paper on the subject of Yucca fertilization, virtually accepting all that I had published thereanent;⁵ but at the conclusion endeavored to complicate and mystify the subject still further, by stating that though his angustifolias had not been fertilized, yet from a single flower he had taken 17 moths, 4 of which were Prodoxus and 13 Pronuba—the only inference being that Pronuba was impotent. He made no mention whatever of my visit or my determinations, and upon asking him for authority for his determinations it turned out that the day after my visit he sent the moths from one of the very last flowers to Dr. Hagen of Cambridge, who determined the specimens to be of both species in the above proportions, but all ♂’s.⁶ Now Hagen knows little outside of Neuroptera and only the year before had made a most unpardonable blunder in pronouncing certain moths, which he had bred from Yucca stems to be Pronuba yuccasella where afterward he confessed they were Prodoxus, and one would suppose that a fair man seeking only the truth would have at least put my own determinations, in relation to genera of my own creation, along side of Hagen’s.⁷

The males are not so easily distinguished as the ♀’s and Hagen may again have blundered; but even if he was correct the explanation is simple: filamentosa was just about blooming and Pronuba consequently just beginning to issue at the time. It is well known to entomologists that the ♂’s precede the ♀’s somewhat in issuing, and the first ones, having no flowers of filamentosa would naturally resort to what was left of angustifolia so that for a day or two both species might be found together. But nothing is more certain, from a series of experiments and observations which I made this past summer, than that Prodoxus ♀ oviposits in the stem and that her race is run essentially by the time the plant begins to bloom, for she can only successfully oviposit in the tender stem and perishes in the act when attempted after the flowers begin to open and the stem gets hard; further that she is absolutely incapable of pollinizing and never attempts it.

In reference to cross-fertilization you have, I believe, misapprehended the facts in supposing that Pronuba ♀ necessarily gathers the pollen from the same flower which she fertilizes.⁸ My language is perhaps ambiguous on this point, but in fact she not only pollinizes with the same load of pollen different flowers on the same panicle, but often flies from plant to plant. I have never seen her gather the pollen, but have watched her thus go from flower to flower and from plant to plant during a single evening and with one and the same load.

I have derived great pleasure and profit recently in glancing over your last work on Earth worms,⁹ and feel thankful to know that your health and faculties yet permit you to do so much not only to advance knowledge but to teach us younger men the true methods of investigation

I am unfortunately a very busy man with time so occupied with domestic and administrative duties that I get little time for pure research: else I should love to write more often and on many subjects.

Please give my best regards to your son Frank who will remember our ocean trip together.¹⁰ With the Compliments of the Season and best wishes for your continued health and strength, | I am | Yours sincerely | C. V. Riley.

Chas. Darwin Esq. | London, Eng.