IV] 



THE LARVA OR NYMPH 



87 



The legs (fig. 34) are always longer than those of the imago, and 

 their bases placed further apart. The coxae (ex) are peculiar in 

 being articulated ventrally with the sternum by means of a special 

 condyle (fig. 29 B, en). The articulation of the femur with the small 

 trochanter is very peculiar, and forms a breaking-joint [40]. The 

 trochanteric muscles, instead of being inserted into the base of the 

 femur, are attached to a stretched membrane which keeps the 

 femur in position. By a sudden contraction of these muscles, the 

 membrane can be broken and the femur released, with scarcely 

 any loss of blood. This process of autotomy enables the larva to 

 escape whenever a leg is seized by an enemy, or gets hopelessly 

 entangled. The hairs present on the legs of almost all young 

 larvae usually disappear in later instars, so that the legs become 

 quite smooth. Some larvae, however, have very hairy legs (fig. 33). 

 The imaginal armature is absent, or only rudimentary, in the latest 

 instars. Small spines are, however, frequently developed distally 

 on the tibia, and on the tarsal joints. In 

 Aeschna, a series of beautiful trident-spines 

 (fig. 34s) is found on the tibia. The tarsal 

 claws are always well-developed, but the tooth 

 found on them in the imago is either absent 

 or rudimentary. 



Interesting specializations in the form of 

 the legs are correlated with special habits in 

 some larvae. Thus, rock-dwelling larvae (e.g. 

 Diphlebia, fig. 35) have broad, flat, blade- like 

 femora which can be closely applied to the 

 rock surface. The burrowing larvae of Gom- 

 phinae have strongly ridged surfaces on femur 

 and tibia, while the tarsi of the fore and 

 middle legs are reduced to two joints (fig. 

 36 A, B). 



The Abdomen (fig. 29 A, B). 



In the larva, the abdomen is always shorter and broader than 

 in the imago, the difference being very pronounced in Libellulidae 

 and some Gomphinae. The segmental sclerites are more easily 

 distinguished. The tergites (A, 5-10, c, 1-2) are always more or 



Fig. 35. Larva of 

 Diphlebia lestoides 

 Selys. (Natural 

 size.) Original. 



