28 THE IMAGO [CH. 



made out a tiny process, the vestige of a plantula, or terminal 

 pad. 



Specializations in the Armature of the Legs. So numerous are 

 the variations in this armature that we can only here mention the 

 most outstanding of them : 



(1) In the Corduliinae and in Orogomphus, a tibial keel (tbc) is 

 present on the under side of the tibia in the male. It is usually 

 only present in the fore-legs. It may be short, and placed at the 

 distal end of the segment, or long, occupying the distal half or 

 more. It seems to be formed by a fusion of the original row of 

 spines which it replaces. 



(2) In some Libellulinae (e.g. the Tetrathemini) the males have 

 a row of curved thorn-like spines on the second and third tibiae. 



(3) In the Cordulegastrinae, each of the original rows of spines 

 on the femur has become double or triple. The femoral spines 

 are very short in this and some other subfamilies, and may be 

 reduced to knobs. 



(4) In many Platycneminae, the males have the tibiae of the 

 middle and hind-legs strongly dilated, with the spines along the 

 flattened edges (fig. 9 B). 



(5) In the Calopterygid genus Rhinoneura, the hind femur is 

 thickly clothed with short dense hairs. 



(6) In the Teinobasini, the inferior tooth of the tarsal claws is 

 absent or vestigial. 



THE ABDOMEN (figs. 1, 10). 



The abdomen of the Dragonfly consists of ten complete and 

 very distinct segments or uromeres, while, according to Heymons 

 [72], the reduced remnants of an eleventh and generally also of 

 a twelfth segment can also be recognized. At its extreme end, 

 the abdomen carries a set of anal appendages. In shape, it is 

 always narrow, and much elongated in comparison with its breadth. 

 Probably the most primitive form was that of a fairly narrow 

 elongated cylinder, without either constrictions or expansions. 

 Such a form is approximately retained to-day in the Petalurinae 

 and many Calopterygidae. In the Pseudostigmatinae (Plate I, 

 fig. 8), the abdomen has become excessively slender, and of enormous 



