FORM, GROWTH, AND CHANGE 39 



In this introductory survey of the life-history of some 

 typical insects, we may pass from that of a grasshopper to 

 that of a dragon-fly, and it will be again convenient to preface 

 discussion of the young stages with a brief, general account 

 of the structure of the adult insect. 



A typical dragon-fly (Fig. 21) is one of the most remarkable 

 of all insect-forms. In these insects we have, to quote a 

 recent authority, 1 "a singularly isolated group, marked by 



FIG. 21. DRAGON-FLY (Acsckna cyanea). 

 Natural size. From Latter " Nat. Hist, of Common Animals ". 



very high specializations of structure, superimposed upon an 

 exceedingly archaic foundation." The dragon-fly's head is 

 broad and prominent, very freely movable on the prothorax, 

 a large proportion of its area occupied with the great sub- 

 globular compound eyes, besides which three simple eyes 

 (ocelli) are present, situated in the centre of the crown. The 

 feelers are short and slender, almost thread-like, with at most 



1 R. J. Tillyard : " The Biology of Dragon-flies ". Cambridge, 1917. 



