252 Annals of tlie South African Museum. 



and the eye tbei-e are small, ronglil\' triangular sclerites, the genae, 

 well developed iji the Gompliinae, small in the other Anisoptera, 

 large but not distinctly limited towards the frons in the Zygoptera. 

 The anteclypeus and postcly|ilens have often been named " nasus " and 

 " rhinarium " respectively ; but the writer always found it difficult to 

 distinguish between the nasus and the rhinarium, since the two terms 

 apply to the same thing in Latin and in Greek respectively ; the 

 significative terms "ante"- and " postclypeus " seem preferable for 

 obvious reasons. 



The antennae are mere rudiments, as shown by our figures ; their 

 value for systematics and description is not important. 



The thorax of Odonata is highly characteristic of the Order, and a 

 wonderfully elaborate adaptation to the needs of an aerial creature 

 that finds its food on the wing, will in very many cases even eat 

 without alighting, will play and mate and sometimes even oviposit in 

 flight. The first thoracic segment, the prothorax, is separated from 

 the two following wing-bearing segments by an extremely loose joint, 

 similar to the joint between head and prothorax ; both these joints are 

 largely moveable in every direction, together giving to the large-eyed 

 head a remarkable freedom of movement. The prothorax as a whole 

 is vei'y small, and its single sclerites not easily recognisable. The 

 other segments, the mesothorax and metathorax, are joined to form a 

 strong and solid unit, compact in outline and with the sutures firmly 

 soldered, so as to form a strong support for the wings as well as an 

 ample box for the vigorous muscles. The specific feature of Odonata 

 in this structure is the reduction of sternites and especially of 

 tergites and the extreme development of the lateral sclerites, the 

 episterna and the epimera of each segment. These lateral sclerites 

 being, moreover, placed with their longer, dorso-ventral axis in an 

 oblique position, the lower end cephalad, the upper caudad, another 

 most important feature of the Odonata thorax results, viz. the 

 throwing forward of the coxae and legs well in front of the wing bases, 

 almost under the head and the mouth. This position of the legs, 

 unique among insects, explains the position of rest adopted by most 

 dragonflies, this position being not one of sitting, but rather of 

 suspension. Also it is in strict correlation with their feeding habits, 

 as Dr. Wesenberg-Lund, of Hilleroed, very justly remarks in a recent 

 paper.* 



The feet have for function the holding of the prey, when, as is rerv 

 often the case, the dragonfly eats an insect just captured without 



* C. Wesenberg-Lund, " Odonaten-Studien," ' Internat. Rev. ges. Hydro- 

 biol.,' 1913, pp. 155-228, 373-422, 



