30 



The Form of Insects 



ancestors of these groups never possessed the power 

 of flying. 



Hind-body.— The hind-body (abdomen) of an 

 insect contrasts strongly with the fore-body. Its 

 segments are, as a rule, closely similar to each other, 

 and, in the adult, never bear legs. Very rarely, as 

 in some Bristletails, do all the segments carry small 

 pairs of limbs. Each segment is protected by an 

 upper sclerite {tergiim) and a lower one (sternum); 

 the side regions {pleura) generally remain soft and 

 membranous. In the male Cockroach ten segments 



Fig. 23. — Outline of Male ( O / and Female \ + ^ Cockroaches from the 

 side, showing abdominal segments (numbered i-io). Magnified 4 

 times. After Miall & Denny. 



are visible above, but the last three are very small ; 

 in the female only eight can be seen ; these are the 

 first seven and the tenth, with which the eleventh is 

 fused, the eighth and ninth being hidden under the 

 seventh (fig. 23). Viewed from beneath, nine 

 sternites can be seen in the male and seven in the 

 female, the eighth and ninth in the latter sex being 

 withdrawn into the seventh. In more highly de- 

 veloped insects, the number of abdominal segments is 

 smaller than in the cockroach, the three or four hind- 



