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less than ten days they reach their full growth, when they cast their skin, and assume the state of a chrysalis, in which immature limbs are plainly discernible. Before they undergo this change, the larva sometimes enclose themselves in an oval, cotton-like covering. In about the same space of time, the chrysalis undergoes its last transformation, when the complete flea exerts its active powers, and feasts upon the first animal to which it can gain access. It prefers the delicate flesh of women or children, and is observed to avoid that of sick persons. This insect is remarkable for the unusual situation of the two fore-legs, which are placed immediately beneath the head. The antennm are short, hairy, and consist of five joints. Beneath these is the proboscis, which is a strong, sharp-pointed tube,. fixed between a pair of jointed sheaths, rendered still stronger at the base by a pair of pointed scales. The eyes are large, round,. and black. The high polish, of the Shelly armour, which is at once a security and a covering, is admirable. The flea loves to nestle in the fur of dogs, cats, rats, &c. It has an astonishing power of leap ing, in proportion to its size, which is effected by the elasticity of its feet, the articulations of which act like so many springs.

The family Acarus, or Mite, forms the next

genus.