One of the most curious peculiarities connected with the bats is their singular parasite, the Nycteribia.[1] On cursory observation, this creature appears to have neither head, antennæ, eyes, nor mouth; and the earlier observers of its structure assured themselves that the place of the latter was supplied by a cylindrical sucker, which, being placed between the shoulders, the creature had no option but to turn on its back to feed. This apparent inconvenience was thought to have been compensated for by another anomaly: its three pairs of legs, armed with claws, being so arranged that they seemed to be equally distributed over its upper and under sides, the creature being thus enabled to use them like hands, and to grasp the strong hairs above it while extracting its nourishment. It moves by rolling itself rapidly along, rotating like a wheel on the extremities of its spokes, or like the clown in a pantomime hurling himself forward on hands and feet alternately. Its celerity is so great that Colonel Montague, who was one of the first to describe it minutely[2], says its speed exceeds that of any known insect, and as its joints are so flexible as to yield in every direction (like what mechanics call a "ball and socket"), its motions are exceedingly grotesque as it tumbles through the fur of the bat. [Footnote 1: This extraordinary creature had formerly been discovered only on a few European bats. Joinville figured one which he found on the large roussette (the flying-fox), and says he had seen another on a bat of the same family. Dr. Templeton observed them in Ceylon in great abundance on the fur of the _Scotophilus Coromandelicus_, and they will, no doubt, be found on many others.] [Footnote 2: Celeripes vespertilionis, _Mont. Lin. Trans_, xi. p. 11.] To enable it to attain its marvellous velocity, each foot is armed with two sharp hooks, with elastic pads opposed to them, so that the hair can not only be rapidly seized and firmly held, but as quickly disengaged as the creature whirls away in its headlong career. The insects to which it hears the nearest affinity are the _Hippoboscidæ_ or "spider flies," that infest birds and horses, but, unlike them, it is unable to fly. Its strangest peculiarity, and that which gave rise to the belief that it is headless, is its faculty when at rest of throwing back its head and pressing it close between its shoulders till the under side becomes uppermost, not a vestige of head being discernible where we would naturally look for it, and the whole seeming but a casual inequality on its back. On closer examination this apparent tubercle is found to have a leathery attachment like a flexible neck, and by a sudden jerk the little creature is enabled to project it forward into its normal position, when it is discovered to be furnished with a mouth, antennæ, and four eyes, two on each side.