THE FLEAS. 99 



part of its length, and has the two apical parts more or less distinctly jointed ; the maxillae are short, 

 nearly triangular pieces at the sides of the mouth, but each of them bears a well-developed four-jointed 

 palpus ; the mandibles are long and thin, with serrated edges, and slightly hollowed lengthwise, so 

 that when brought together they form a sheath for an unpaired organ (regarded as the same as the 

 epipharynx of the Diptera), which somewhat resembles a three-cornered sword-blade, and is used for 

 the same purpose, namely, that of piercing the flesh and shedding the blood of the bearer's victims. 

 This three- cornei'ed weapon is very deeply channelled below. It is, as already stated, enclosed between 

 the mandibles ; the long, cleft, membranous labium embraces these, and the whole constitutes an 

 admirable apparatxis for sucking up the blood set free by the puncture of the central piercing organ. 

 The abdomen, which consists of eight segments, is covered, like the rest of the body, with a horny 

 integument, and the hinder edges of all the segments, as also of the scales supposed to represent the 

 wings, are garnished with rows of bristle-like hairs. The legs also are bristly. 



It will be seen that in the principle of action of the mouth the Fleas undoubtedly resemble the 

 Diptera, but on the other hand the two divisions of the labium are generally distinctly jointed, and 

 evidently represent labial palpi, and thus, as Dr. Gerstacker says, these insects form a distinct 

 transition towards the next order (Rhynchota), as also by the segmentation of the body, and espe- 

 cially of the thorax, towards the Orthoptera, " so that they may be characterised as aberrant Diptera, 

 with partial Orthopte- 

 rous and Hemipterous 

 characters." Insects so 

 characterised are surely 

 best placed in a niche 

 by themselves. 



In their transfor- 

 mations, however, the 

 Fleas present another 

 resemblance to the 



Diptera, and especially METAMORPHOSES OF THE COMMON FLEA. 



to the earlier families 



of the order. The eggs, which are usually not numerous, are deposited by the female in suitable 

 places for the development of the larvae, such as obscure, dusty corners, among the hairs or 

 feathers of the animals infested, or upon the articles on which these animals customarily lie. 

 Thus these "nits" may always be found in the beds of House Dogs and Cats. From the eggs 

 the larvae are speedily hatched. They are long, worm-like, footless grubs, showing thirteen 

 distinct segments, garnished with fine bristle-like hairs. The head is slightly horny, furnished 

 with a pair of short antennae and a mouth with biting organs, and the last segment is 

 provided with a pair of horny hooks. These larvae are active, twisting about in every direction, 

 and feeding upon the nutritious parts of feathers and other refuse animal matter among 

 which they live. In warm weather the larvae are soon mature (twelve days is the average 

 time in the case of the common Flea), and they then usually enclose themselves in a small silken 

 cocoon, and there undergo the change to the pupa state. The pupa is quiescent, with the different 

 parts enclosed in special cases, and the period during which the insects remain in this condition is 

 usually about equal to that of their larval existence, except in the case of those inhabiting cold and 

 temperate climates, many of which pass the winter in the pupa state. 



The perfect insects, as is well known, feed upon the blood of warm-blooded animals, and, as a 

 rule, each species of Flea is allotted to some particular species or group of species of mammals or 

 birds. The insects conceal themselves among the hairs or feathers of the animal on whose blood 

 they are destined to feed, and generally stick to this comfortable and convenient dwelling-place for 

 the remainder of their joint lives, but it is curious to see how soon after the host is killed the 

 parasites escape from its body and show manifest signs of perturbation. The commen Flea (Pulex 

 irntans) is the best known species, from its habit of di-awing its supplies of food from our own 

 persons. The Fleas of the Dog and Cat are distinct (P. canis and P. felis), and are chiefly confined 

 to those animals, although they do not disdain to vary their diet occasionally with human blood. 



