[Illustration: 20.--Human Flea (_Pulex irritans_), after Blanchard.] Fleas of a brown colour, almost black, and of enormous size, are commonly met with on the sandy shores of the Mediterranean, at least, in the neighbourhood of Cette and Montpellier; they are more than half as large as a common fly. These are human fleas, and their presence on the sea-shore during the heats of summer is due solely to the great number of bathers of both sexes and of all classes, which lay their clothes down there. If at some future day these insects were to be placed in the rank of surgical species, it would be necessary to resort to those shores in order to procure them; and we might suppose that, by judicious crossing, we might soon produce races that would be of real service; as yet, however, the therapeutic art has had 129 recourse only to leeches. Since we have seen these insects harnessed and performing their exercises in public, we cannot say that the future may not reserve for us a still greater surprise. None who saw them can have forgotten the exhibition of learned fleas made by a young lady who had sufficient patience to train them. Walckenaer saw them in Paris, and examined them with the eye of an entomologist; he relates that thirty fleas performed their feats at evening exhibitions, for admission to which the sum of sixty centimes was paid; that these fleas stood on their hind legs, armed with a pike, which was a very thin splinter of wood; some dragged a golden chariot, others a cannon with its carriage, and all were attached by a golden chain on the thighs of their hind legs. It is curious to see how Leeuwenhoek described, two centuries ago, the history of the flea, with all its details, the accuracy of which can scarcely be surpassed. He observed their entire anatomy, as far as was possible with the instruments of his time (1694), and his descriptions are accompanied by excellent plates; he saw them copulate and lay eggs, and followed their whole development. The finest fleas, both as to their size and form, inhabit the bats. Fleas are often found on horses. A colonel of cavalry, on his return from the frontier in 1871, sent me some of these insects, with the request that I would examine them. He added that the horses of his regiment were literally eaten up by them. It was the _Hematopinus tenuirostris_. There is a species peculiar to monkeys, which Mons. Paul Gervais has described under the generic name of _Pedicinus_.