324 THE MICROSCOPE. 



therefore difficult to take. The following is generally the plan resorted 

 to : sprinkle a little oatmeal on a piece of black paper near their 

 haunts ; after a few hours, remove it carefully to a large glazed basin, 

 so that when they leap from the paper, as they will when brought to 

 the light, they may fall into the basin, and thus become separated from 

 the meal. The best way of separating the very fine scales from their 

 bodies has been previously explained (See page 44). The markings 

 cannot be seen with a lower power than a quarter-inch object-glass. 

 Under a power of 500 diameters, the surface appears to be covered 

 with extremely delicate wedge-shaped dots or scales, as seen at No. 5 a, 

 Plate X. The smaller scales are much more difficult to resolve than 

 the larger ; and they form a good test of the defining power of a l-8th 

 or 1-1 2th object-glass, No 8, a portion of a large scale of Lepisma 

 sacclmrina, showing the longitudinal markings. 



The family Aphaniptera, in which the metamorphosis is what is 

 termed complete the larva, pupa, and imago being very distinct in 

 their appearance : the well-known flea is the best example of this small 

 group. By many recent authors these insects have been arranged with 

 the Diptera, which would appear to be incorrect, as they differ in many 

 particulars. The external covering of the flea (fig. 156) is a horny case, 

 formed of very distinct segments ; those of the thorax being always 

 disunited. Although apparently apterous, the flea has the rudiments of 

 four wings, in the form of horny plates on the sides of the thoracic 

 segments. Its mouth consists of a pair of sword-shaped, finely-serrated 

 mandibles, which, with a sharp, needle-like organ, appears to constitute 

 the formidable weapon 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 antenna, or horns, its proboscis, and a pair of sharp lancets, with 

 which it penetrates the skin. On each side of the head a large sharp 

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

 two sharp-hooked claws, which are so constructed, that they can be 

 folded up, as it were, and when it leaps it springs them out ; so that 

 its whole strength is excited at the same moment. The female flea, 

 fig. 156, lays a great number of eggs, sticking them together with a 

 glutinous matter ; those of fleas infesting the dog or cat are made fast 

 to the roots of the hairs ; in four days' time the eggs are hatched, 

 and a small white worm or grub is seen crawling about, and feeding 

 most actively. No. 4, fig. 157, is a magnified view of one ; it is 

 covered with short hairs, which prevent its being easily dislodged. 

 After remaining in this state about nine or ten days, it assumes the 



