FLEA, a name given to insects forming the scientific order Siphonaptera (or Aphaniptera) and typically applied to the human flea (Pulex irritans). Fleas live as ecto-parasites on the bodies of mammals and birds, where they feed by sucking the blood. They are remarkable for their powers of leaping, and about Soo species are known. They are wingless insects with the body laterally corn pressed, short stout antennae reposing in grooves, and the eyes minute or wanting. The mouth-parts are adapted for piercing and sucking. The skin of the host is perforated by the blade-like man dibles, and the blood is imbibed through a channel formed by these organs in close conjunction with the stylet-like labrum. Fleas pass through a complete metamorphosis : their larvae are worm like, and live on organic refuse about the lairs of the hosts, and the pupae are enclosed in silken cocoons. The human flea is nearly cosmopolitan and, in addition to man, it also infests certain other mammals. The eggs are found on the floors, carpets, etc., of un cleanly dwellings, where the larvae feed upon particles of refuse, and the whole life-history is completed in f our to six weeks. Sev eral species of fleas infesting rats, and also known to suck the blood of man, are concerned with the spread of the bacillus of bubonic plague, the most important being Xenopsylla cheopis, which is the chief plague flea in India. In the "jigger" or "chigoe" (Der matophilus penetrans) of the tropics the female becomes em bedded in the skin of the feet of man and other hosts, where she becomes distended to the size of a small pea, and causes extreme irritation. (A. D. I.)