8 Dragon-Flies : their Life-History. [Sess. 



enormous hypertrophied pieces which form the " palpi," and 

 which are often furnished at the tips with an articulated 

 spine, or terminal joint, the whole structure serving to retain 

 the prey. 



The eyes of the dragon-fly are, as a rule, enormous, forming 

 two rounded masses, often contiguous, which means that they 

 extend all round the head, from one angle of the mouth to the 

 other, and occupy a large proportion of its surface. In fact, 

 many of them possess what mortals often covet — eyes on the 

 back of their head. Sometimes they are widely distant, as in 

 Agrionidte and Gomphina. They are compound, being com- 

 posed of innumerable hexagonal facets, of which as many as 

 12,544 have been counted in one eye. The chitinous skin 

 which covers the whole body is continued over the eye as a 

 transparent layer or cornea, and it is this that is so divided. 

 On examination they are seen to be unequal in size, the facets 

 being larger on the upper portion. Over and above these 

 compound eyes, and aiding them largely in their function, 

 there are three ocelli or simple eyes, and these when present, 

 which they usually are, are placed on the forehead, looking in 

 different directions and in the form of a triangle, thus giving 

 the creature practically a complete circle of vision. 



The prothorax is very small, and consists of only a narrow 

 ring, the upper portion of which is frequently raised into lobes. 

 The thorax, carrying the wings and legs, is large, and consoli- 

 dated into a single piece, exhibiting, as it should, great strength. 

 There are oblique sutures on the sides below the wings, and 

 the portion in front of them, which is extremely strong, shows 

 a median carina or keel above and a broad transverse sinus 

 posteriorly. 



The abdomen, compared with the other primary segments, 

 is of great length, and varies considerably in form, the two 

 extremes being the filiform structure seen in the Agrionidae, — 

 many of them being much thinner than a darning-needle, — 

 and the broad and depressed form seen in Libellula depressa. 

 It consists of ten distinct segments, whereof the basal two and 

 those at the apex are short, the others lengthened, the first 

 being excessively short. That of the male terminates in pre- 

 hensory appendages known as " claspers," and these are some- 

 times so prominent as to have been taken for stings. 



