INSECTS. 513 



No. 5, the longitudinal markings are shown under a lower 

 power. 



The Lepisma have a spindle-shaped body, usually covered 

 with silvery scales, and furnished along the sides of the 

 abdomen with a series of appendages or false feet, besides 

 several long-jointed bristle-like organs at the extremity. 

 The head is concealed under a pro-thorax ; the eyes are 

 usually compound, and frequently occupy the whole of the 

 head. The antenna are very long, and composed of 

 numerous joints; the maxillary palpi, which consist of 

 from five to seven joints, are very conspicuous. These 

 insects generally inhabit moist places. The most common 

 species, Lepisma saccharina, is frequently found about 

 houses, especially in sash-frames, or in old sugar-casks ; 

 from the latter it derives its name. The scales from these 

 little insects (Fig. 249, No. 8) have ever been favourite 

 objects with microscopists, and generally used for testing 

 the power of penetration and definition of the instrument 

 itself. 



The metamorphosis is complete in the Suctoria, or 

 Siphonaptera, a wingless family the larva, pupa, and 

 imago of which are very distinct in their appearances 

 the well-known Flea is the best example of this small 

 group. By many authors these insects have been arranged 

 with the Diptera; this would appear to be incorrect, as 

 they differ in many particulars. The external covering 

 of the Flea (fig. 268) is a horny case, divided into distinct 

 segments; those upon the thorax being always disunited. 

 Although apterous, the Flea has the rudiments of four 

 wings, in the form of horny plates on both sides of the 

 thoracic segments. Its mouth consists of a pair of sword- 

 shaped mandibles, finely-serrated; these, with a sharp, 

 needle-like organ, constitute the formidable weapons with 

 which it pierces the skin of its victim. 



The neck is long, the body covered over with scales, the 

 edges of which are set with short spikes or hairs ; from its 

 head project a pair of antennae, feelers or horns, a pro- 

 boscis, which forms a sheath to the pair of lance- shaped 

 weapons. On each side of the head a large compound 

 eye is placed. It has six many-jointed powerful legs, 

 terminating in two hooked claws ; the pair of long hind 

 L L 



