76 THE LARVA OR NYMPH [CH. 



fi 1 t, while that of the first moves up into the metathorax. In 

 t 3 imago, the latter is attached posteriorly to the ganglion of 

 metathorax. 



11. Increase in the number of Malpighian Tubules. There are 

 only three in the newly-haiched larva. These increase at each 

 ecdysis, until a total of fifty or more is attained. 



The full-grown Larva (fig. 29). 



We may now compare the structure of the full-grown larva 

 with that of the imago (chap, n), using one of the large Aeschninae 

 for principal reference. 



The Head. 



The eyes are smaller, and placed more anteriorly in the larva. 

 Consequently the epicranium (ep) is much larger, especially the 

 occipital portion, which expands laterally into two very prominent 

 postocular lobes. The frons (fr) is clearly marked off, and shews 

 the* frontal ridge in the Anisoptera. The clypeus (cl) is undivided, 

 the labrum (Ibr) well-formed. The antennae (ant) are longer and 

 more functionally important than in the imago. Fig. 2 shews 

 some interesting variations in their structure. The ocelli may be 

 barely indicated on the flat expanse of the epicranium (Aeschninae) 

 or they may be clearly marked (Zygoptera). The mandibles and 

 maxillae closely resemble those of the imago, except in Pseudo- 

 phaea and Cora, where the larval mandibles are biramous [31]. 



Structure of the Labial Mask (figs. 29-32). 



The chief difference between the head of the larva and that of 

 the imago is undoubtedly the structure and function of the labium. 

 In the larva, this has become a highly specialized and very efficient 

 organ for the capture of prey, unique in the Animal Kingdom. 

 This organ is known as the mask (figs. 29, 30) because it hides the 

 other mouth-parts, and sometimes even covers up the whole face. 

 Its formation is chiefly due to a great lengthening of the mentum 

 and sub-mentum. These come to function much like the fore- 

 arm and arm of the human fore-limb, while the palps are opposed 



