BOOK-LOUSE AND SILVER-FISH INSECT 307 



powers; the habits of the insect, however, do not bear 

 out this indication. The remaining part of the legs is in 

 each case slender and almost transparent, and the feet 

 consist of three joints only, terminated by the usual pair 

 of claws. As with some other of our household insects, 

 no wings are developed, though most species of the 

 group to which it belongs have the full complement. A 

 long, stout, but soft-skinned abdomen succeeds the thorax, 

 a little broader behind than in front, and bluntly rounded 

 at the end, where a few bristles project. 



Very little change takes place in the form of the 

 insect during the course of its life, and it is at all times 

 active, never losing its limbs to become a quiescent chrys- 

 alis, and belonging therefore to that section of the class 

 Insecta in which the metamorphosis is incomplete, the 

 division to which the cockroach and bed-bug also belong. 

 When quite young it has but two joints to its feet, 

 instead of three, and at the same time the number of 

 joints in the antennae is smaller than when fully grown. 



As regards systematic position, it belongs to a family 

 which includes several insects that are extremely abun- 

 dant, but at the same time almost entirely unknown to 

 any but professed entomologists, and hence have no 

 popular names. The family is called Psocidce, and most 

 of our British species are pretty little winged creatures 

 of delicate structure, in appearance something like 

 Aphides, or plant-lice. Some are found in profusion 

 running about over palings and fences, or on the trunks 

 or branches of several kinds of trees, especially those of 

 the pine and fir tribe. If the branches of a larch or 

 Scotch fir, for example, be shaken over a sheet of paper, 

 numbers of little creatures belonging to this family will 

 fall out. The family Psocidve, again, is reckoned as 

 comingjwithin the domain of the order Neuroptera (nerve- 



