jypiA N DliAGONFLIKS. 



461 



Simplitieil nomunclatiiru. 



Discoidal tiolil. 



(.■\ibital space. 



Cubital nervuros. 



'^viX ni'i'vure. 



4th norvnre. 



Ath uorvnro. 



/ia (supplementary nervure). 



(itli nervure. 



7th nervure. 



7a (supplementary nervure). 



<*>th nervure. 



9th nervure. 



Arc. 



Anal Held. 



Stigma. 



Membrane. 



The Let/s. (Plate I.) 



The legs consist of the usual 

 coxa, trochanter, fennir, tibia 

 segments and ending in a 

 furnished on their inner 



five parts found in 

 and the tarsns, the 

 pair of hooked claws 

 sides with minute 



insects, that is, the 



latter having three 



or inigues which are 



hooks, these latter 



differing in size with the species. The femorto and tibite are usually fur- 

 nished with one or two rows of stout or fine and long or short spines and 

 one or two rows of cilite, varying in size and usually gradually increas- 

 ing in length from the proximal to the distal ends. The legs are only 

 used for resting, never for walking but they perform an additional and an 

 important function by assisting Lo seize the insects prey. This they do 

 whilst Hying, all the legs being sloped forward, the ends held at an equal 

 distance apart so as to form a sort of ribbed net with a circular opening 

 in which the nisects which form the food of the Dragonfly are swept up. 



The Ahdomrn. (Plate I.) 



The abdomen is made up of ten segments and is markedly polymorphic. 

 In most of the Libellulines. the abdomen is comparatively short, somewhat 

 depressed or compressed, often tapering from the base to apex, or clavate or 

 fusiform in shape : in the Aeschnincs. the base is often more or less tumid 

 and subsequently somewhat constricted, after which it is again slightly 

 dilated and of an uniform thickness as far as the anal end : in the ^J'gop- 

 teridic, the abdomen is very long and very slim, uniformly cylindrical and 

 with parallel sides : in another genus (Acisoma), the basal segments are 

 much dilated whilst the terminal are extremely attenuated, in some of the 

 Oomphines and a few of the Libellulines, the borders of the Sth and 9th 

 segments may show broad, lateral expansions, whilst most of the former 

 possess a small tubercle on either side of the 2nd segment. The mid-dorsum 

 is often strongly keeled and the ventral surface more or less Hat. Along 

 the middle line of the latter, the ventral plates will bo seen to be split, 

 their free borders being connected hy a delicate, black membrane, the 

 " pleural membrane ", which runs from the :>rd to the Hth segment. 

 The ventral plates overhang the membrane, which is tucked in beneath 

 their free or overhanging borders. If a living dragonfly be observed, 

 its abdomen will be seen to rhythmically expand and contract, this move- 

 ment being permissible owing to the splitting of the ventral plates below 

 and the interposition of the pleural membrane. The function then of this 

 interesting structure is to allow expansion and contraction of the abdominal 

 walls, by which an alternating negative and positive pressure is induced, 

 the effect of which is to suck in and force out, air from the thoracic spiracles. 

 18 



