BOOK-LOUSE AND SILVER-FISH INSECT 305 



being probably few from which it is entirely absent. 

 Its minuteness, however, is an effectual means of con- 

 cealment, and its presence is usually unknown and 

 unsuspected. 



The accompanying illustration (Fig. 102) will give an 

 idea of its form, but it is so small that no details of 

 figure can be definitely made out in 

 a living specimen except by aid of a 

 lens, its length when full-grown not 

 exceeding one-twentieth of an inch. 

 Hence it is hardly likely to be 

 recognised from its portrait, except 

 by those who are accustomed to the 

 constant use of the hand-lens, for to 

 the naked eye it appears as little 

 more than a rapidly gliding short 

 streak, or an animated scrap of 

 thread. It is semi-transparent, and 

 has little colour except when mature, 

 at which time a brownish grey or smoky tint is per- 

 ceptible over its back. The head is remarkably large 

 when compared with the body, and carries, amongst 

 other organs, two long, many -jointed antennae of 

 wonderful thinness, finer than the most delicate of 

 hairs, and a small pair of black eye -masses, one at each 

 side, inclining towards the upper surface, and not at all 

 prominent. 



The front of the head is 

 considerably swollen above, a 

 feature which becomes evi- 

 dent when a profile view is 

 obtained (Fig. 103). Its ex- 

 treme tip, or nose, as it is sometimes called, has a ruddy 

 tinge. A pair of palpi, which, like the antennae, are in 



FIG. 102. Book-Louse 

 (Atropos divinatoria). 



FIG. 103, Side View of Head of 

 Book-Louse. 



