My dear Romanes,--I have been thinking about Pompilius and its allies. Please take the trouble to read on 'Perforation of the Corolla by Bees,' p. 425 of my Cross Fertilisation to end of chapter. Bees show so much intelligence in their acts, that it seems not improbable to me that the progenitors of Pompilius originally stung caterpillars and spiders, &c., in any part of their bodies, and then observed by their intelligence that if they stung them in one particular place, as between certain segments on the lower side, their prey was at once paralysed. It does not seem to me at all incredible that this action should thus become instinctive, _i.e._ memory transmitted from one generation to another. It does not seem necessary to suppose that when Pompilius stung its prey in the ganglion that it intended or knew that the prey would long keep alive. The development of the larvæ may have been subsequently modified in relation to their half-dead instead of wholly dead prey, supposing that the prey was at first quite killed, which would have required much stinging. Turn this notion over in your mind, but do not trouble yourself by answering. Yours very sincerely, CH. DARWIN. N.B. Once on a time a fool said to himself that at an ancient period small soft crabs or other creatures stuck to certain fishes; these struggled violently, and in doing so, discharged electricity, which annoyed the parasites, so that they often wriggled away. The fish was very glad, and some of its children gradually profited in a higher degree and in various ways by discharging more electricity and by not struggling. The fool who thought thus persuaded another fool to try an eel in Scotland, and lo and behold electricity was discharged when it struggled violently. He then placed in contact with the fish, or near it, a small medusa or other animal which he cleverly knew was sensitive to electricity, and when the eel struggled violently, the little animals in contact showed by their movements that they felt a slight shock. Ever afterwards men said that the two fools were not such big fools as they seemed to be. STULTUS. _From G. J. Romanes to C. Darwin._ 18 Cornwall Terrace, Regent's Park, N.W.: Sunday, March 1881. I have got a lot of cats waiting for me at different houses round Wimbledon Common, and some day next week shall surprise our coachman by making a round of calls upon the cats, drive them several miles into the country, and then let them out of their respective bags. If any return, I shall try them again in other directions before finally trying the rotation experiment. I am also getting the experiment on flashing light agoing. The first apparatus did not answer, so now I have invested in a large eight-day clock, the pendulum of which I intend to make do the flashing. 18 Cornwall Terrace. Regent's Park, N.W.: March 24, 1881.