370 



PHYLUM ARTHROPODA 



General Characters 



Like other Arthropods^ Insects have segmented bodies, 

 jointed legs, chitinous armature, and a ventral chain of 

 ganglia linked to a dorsal brain. Compared zvith Peripatus 

 and Myriopods, adult insects show concentration of the body 

 segments, decrease in the number and increase in the quality 

 of the appendages, and wings in the great majority. 



Insects are terrestrial and aerial, and rarely aquatic 

 animals ; usually winged as adults, breathing by means of 



Fig. 209. — Female cockroach 

 (P. orientalis). 



Fig. 209A. — Male cockroach 

 (P. orientalis). 



trachece, and often with a metamorphosis in the course of their 

 life-history. 



The body is divided into three distinct regions — head, 

 thorax, and abdomen. The head bears a pair of pre-oral 

 antennce, and three pairs of mouth appendages ; the thorax 

 bears a pair of legs on each of its three segments, and, typi- 

 cally, a pair of wings on each of the posterior two ; the abdomen 

 has no appendages, unless these be represented by stings, 

 ovipositors, etc., or else by vestiges. 



First Type of Insects, Periplaneta (or Blatta). — 

 The Cockroach 



Habits. — The cockroaches in Britain are immigrants 

 from the East (P. orientalis), or from America (P. americana). 



