Hind-body — Nerves 31 



most being often retracted and concealed, or absent. 

 In both sexes of the cockroach the first sternite is 

 very much reduced, and the second is cut into on 

 either side in front, on account of the backward 

 direction of the hind legs. In the male the sternites 

 from the third to the seventh are alike four-sided, 

 broad and short ; the eighth is much shorter, while 

 the ninth is rounded behind. In the female, the 

 third, fourth, fifth and sixth segments are similar, 

 while the seventh is very large and ends in a blunt 

 point, its hinder region being split lengthwise to 

 allow the expulsion of the egg-capsule. The ninth 

 segment in the male bears a pair of small simple limbs 

 (stylets), while the eleventh, in both sexes, carries a 

 pair of spindle-shaped limbs of sixteen segments 

 {cercopods). In some insects — such as Bristletails, Stone- 

 flies andCrickets — the cercopods are long and composed 

 of numerous segments ; in the Dragonflies they are 

 hard, leaf-shaped plates. Occasionally the append- 

 ages of the eighth, ninth, or tenth segment form 

 cercopods. The modification of the hinder segments 

 in both sexes is specially concerned with the breeding 

 function, and we shall give further attention to these 

 segments and to certain parts of the skeleton con- 

 nected with them when we consider the reproductive 

 organs. Surrounding the vent (anus) are the small 

 sclerites of the twelfth abdominal segment, the ter- 

 gum and sternum being each divided into two lateral 

 plates (I, 59a). 



Nerves. — Insects, like most other animals, receive 

 sensations from the outside world, and control the 

 movements of the various parts of their bodies by 

 means of a system of nerve-centres and cords, which 

 get impressions from the sense-organs and stimulate 

 or restrain the muscles. Nervous tissue, examined 

 microscopically, is found to be made up of nerve-ceUs 



