CHAPTER II 



THE IMAGO. EXTERNAL FEATURES AND SKELETON 



In this chapter we shall deal with the general external features 

 of the Dragonfly, the exoskeleton of the head, thorax, and abdomen, 

 its internal prolongations or endoskeleton, and all the appendages 

 except the wings, which are treated separately in chap. in. 



THE HEAD (fig. 1). 



The head of a Dragonfly, like that of other insects, shews no 

 clear traces of metameric segmentation. Embryology, however, 

 tells us that it consists of a number of segments, most probably 

 six, which can be classified according to their position with regard 

 to the mouth, and the nature of the nerve-centres supplying their 

 appendages. The following table shews us at a glance the usually 

 accepted theory of head-segmentation : 



No. of 

 Segment 



/'First 



-I 



B J \ Second 



^ OH 



Third 



Position Appendages, etc. 



Preoral Compound Eyes 1 , Lateral 

 Ocelli 1 



Antennae, Median Ocellus 1 



Intercalary segment, with 



no appendages 



Central Nervous System 

 Protocerebrum 



Deutocerebrum 

 Tritocerebrum 



Brain, or 



Supra-oesophageal 

 Ganglion 



Fourth Postoral Mandibles 



Fifth 

 Sixth 



First Maxillae ... 



Second Maxillae (= La- 

 bium) 



First Pair of Ventral 

 Ganglia 



Second Pair of Ven- 

 tral Ganglia 



Third Pair of Ven- 

 tral Ganglia 



Sub- 



oesophageal 

 Ganglion 



1 Generally agreed upon as not being true appendages. 



