XVIII DRAGON-FLIES 413 



reached by any other Insects. It consists of ten segments and 

 a pair of terminal calliper-hke or flap-like processes of very 

 various sizes and forms. 



The wings of the dragon-flies are usually transparent and 

 provided with a multitude of small meshes. The hind wings 

 are about as large as the front pair, or even a little larger ; the 

 main nervures have a sub-paraUel course, and are placed in 

 greater part on the anterior region of each wing. The relations 

 of the more constant nervures and the cells of which they are 

 parts form a complex subject, and are amongst the most im- 

 portant of the characters used in classifying these Insects. The 

 wings are always elongate in comparison to their breadth and 

 have no folds ; they are held partially extended, or are placed 

 so as to project backwards, or backwards and outwards. They 

 exhibit another peculiarity, inasmuch as the front or costal 

 margin is slightly uneven before or near the middle, giving 

 rise to an appearance such as might result from the breaking 

 and subsequent mending of the marginal rib at the spot in 

 question, which is called the nodus. In some forms a pecuhar 

 character exists in the shape of a small opaque space called the 

 membranule, lying close to the body of the Insect in the anal 

 area of the wing, as shown in Fig. 260. 



The legs are slender and are chiefly remarkable for the 

 beautiful series of hair-like spines with which they are armed, 

 and which in some forms {e.g. Platycnemis, Fig. 264) are of 

 considerable length. We beUeve that the legs are of great 

 importance in capturing the prey, they being held somewhat 

 in the position shown in Fig. 262, C. The tarsi are three- 

 jointed. In the male of Lilellago caligata the legs exhibit a 

 remarkable condition, the tibiae being dilated, and on the upper 

 side of a vivid red colour, while below they are white. This 

 coloration and form are each unusual in the family. The male 

 of Platycnemis pennipes, a British species (Fig. 264), shows a 

 similar dilatation of the tibiae, but to a less extent and without 

 any great difference in the colour of the two faces of the dilata- 

 tion. This dilatation reaches its maximum in Psilocnemis 

 dilatipes M'Lach. The position of the legs in relation to 

 the other parts of the body is peculiar to the dragon-flies ; the 

 legs seem to be unfit for walking, the Insects never using them 

 for that purpose. 



