CHAPTER XIV 



THE SUBPHYLUM INSECTA (HEXAPODA) 



Tracheate Arthropoda in which the body is divided into three distinct 

 regions, the head, thorax and abdomen. The head consists of six 

 segments and there is a single pair of antennae ; the thorax consists 

 of three segments with three pairs of legs and usually two pairs 

 of wings ; the abdomen has typically eleven segments and does not 

 possess ambulatory appendages; genital apertures situated near 

 the anus (Fig. 286). 



th. 



Fig. 286. Lateral view of a grasshopper to show external segmentation 

 typical of insects. From Metcalf and Flint, ab. abdomen; an. antenna; ex. 

 coxa ; e. eye ; fe. femur ; hd. head ; th. thorax ; ti. tibia ; to. trochanter ; ts. tarsus. 



The head is enclosed by an exoskeleton which consists of several 

 plates or sclerites, both paired and unpaired, united together, having 

 no clear relation to the segmentation of the head. The segments are 

 indicated by the paired appendages, the ganglia of the nervous system 

 (neuromeres) and the coelomic sacs which can be demonstrated in 

 sections of the embryo but which disappear later. Thus the six seg- 

 ments are indicated by the evidence which follows : 



