BOOK-LOUSE AND SILVER-FISH INSECT 317 



delicacy of their structure. When complete, they are 

 about two-thirds the length of the body. There are also 

 two little black heaps of 

 eyes, one at each side. 

 The usual mouth parts 

 are present, and there are 

 two pairs of palpi the 

 maxillary, five - jointed, 

 and the labial, four- jointed 

 (Fig. 107). The mandi- 

 bles, or biting jaws (Fig. 

 1 08), are long and narrow, 

 and toothed at the free 

 end with several hard 

 prominences. All three 

 thoracic segments are of 

 large size, being, in fact, 

 both the widest and long- 

 est segments in the whole insect. The prothorax is the 

 largest of the three, in marked contrast to the last pest 

 we considered, the book-louse, where it 

 was the smallest. Each of these three 

 segments, as usual, carries a pair of legs, 

 consisting of the customary parts, and 

 each terminated by a pair of claws. No 

 wings are ever developed, nor are any 

 traces of such organs ever perceptible. 

 The abdomen consists of a series of seg- 

 ments tapering gradually towards the tail, 



,-, i i ,1 FIG. 108. Mandi- 



the last one carrying three long, bristle- b ie of Lepimia. 

 shaped appendages. The skin is of a ( AfterLubl 

 delicate texture, and is covered with multitudes of 

 minute iridescent scales of exquisite structure (Fig. 109), 

 closely resembling those of butterflies, and readily 



FIG. 107. A. Labium and Palpi of 

 Lepisma. B. Maxilla and Palpus 

 of ditto. (After Lubbock.) 



