IV] THE LARVA OR NYMPH 73 



towards the river, it eventually jumps into the water. There it 

 floats with its dorsal surface downwards. The free larva emerges 

 much in the same way as in Anax (fig. 26 B). 



Other Forms of Young Larva. In the Libellulidae (fig. 27) the 

 general appearance differs greatly from that of Anax. The eyes 

 are small and black, the head rather squarish; the legs and the 

 short abdomen are more or less hairy. The cerci are short. In 

 the Zygoptera (fig. 28) the larva is much slenderer, the head not 

 unlike that of the Libellulidae, the abdomen almost cylindrical, 

 slender and elongated, the legs hairy. The three caudal gills are 

 usually of equal length, and often longer than the abdomen. They 

 are slender pointed processes, almost filiform, and very hairy. 

 They do not appear to be efficient organs of respiration. 



Larval Growth: Instars and Ecdyses. 



The growth of the larva is marked by a number of stages or 

 instars, separated by the act of ecdysis, or casting of the cuticle. 

 At each ecdysis, not only the outer cuticle, but also all its internal 

 prolongations, are cast off. Thus the linings of the stomodaeum 

 and proctodaeum (chap, xn) including the armature of the gizzard 

 and the intimae of the tracheal trunks, are all cast off at this 

 crisis, and are renewed by the cells underlying them. 



The number of instars is not constant, either for different species 

 or for individuals of the same species. It varies between eleven 

 and fifteen, the pronymph being reckoned as the first. The larva 

 may reach maturity within one year of hatching (most Zygoptera, 

 many Libellulidae, and Anax}, or it may take two years, as in 

 Aeschna, or even from three to five. External conditions, such as 

 drought, warmth, etc., affect not only the length of larval life, but 

 also the total number of instars. It took me three years to rear 

 the larva of Austrocordulia, already more than half-grown when 

 I found it. 



The changes which take place during larval growth may be 

 briefly summarized as follows : 



1. Increase in size of the compound eyes. The number of 

 facets increases at each ecdysis. The eyes never meet on the top 

 of the head (as in many imagines) ; but, in the case of Anax, they 



