IV] THE LARVA OR NYMPH 71 



large and well-formed, but the tarsi are unjointed. Each tarsus, 

 however, ends in two strong claws. The abdomen ends in two 

 strongly-pointed hairy cerci (E, c) above which a rudimentary 

 appendix dorsalis (E, ad) can be distinguished. The mid-gut 

 extends from the first to the fifth segment of the abdomen. It 

 encloses a large barrel-like plug of yolk, which provides nourish- 

 ment for the young larva, and is gradually absorbed, the large 

 vitellophags composing it (p. 235) breaking up, and becoming 

 replaced by the cells of the permanent epithelium. The ventral 

 nerve-cord has a pair of large ganglia in each of segments 1-8, 

 connected by exceedingly short cords (fig. 58). 



The newly-hatched larva is the second larval instar, the first 

 being the pronymph. Reasons for the quick casting of the first 

 larval skin are not far to seek. Firstly, as the embryo ruptures 

 its amnion at an early stage (p. 238), the formation of a cuticle 

 provides a protection in place of the amnion. Secondly, the 

 secretion of a second cuticle within the first uses up a large 

 amount of waste-products which could not otherwise be disposed 

 of, and thus aids the process of excretion. Thirdly, at the first 

 instar or pronymph stage, the labium has not become sufficiently 

 developed to act as a weapon of prehension. By abbreviating 

 the first instar, the larva practically emerges from the egg fully 

 equipped for the struggle of life. 



Variations in the Process of Hatching. 



Most Dragonflies hatch out much in the same way as Anax. 

 Balfour-Browne [5] has described the emergence of the larva of 

 Agrion pulchellum. This differs from that of Anax only in the 



Fig. 25. "Dragonfly -galls" in an osier stem (natural size). Original drawing by 

 P. Tillyard from specimen lent by Mr K. J. Morton. 



increase of the pulse to 100 per minute, and in the fact that the 

 pronymph stage lasts for two or three minutes. The escape from 

 the egg-shell, and again from the pronymphal sheath, does not 

 seem to be so easily accomplished as in Anax. 



