BY R. J. TILLYARD. 



609 



sinole main trachea lies latero-ventrallv, on the inner side of tlie 

 gill. Neither definite blood-canals, internal laminjv, nor alveolar 

 ineshwork are developed. 



The nerve-supply can 

 be followed with diffi- 

 culty from the eightli 

 ganglion to the bases of 

 the gills, but cannot be 

 seen in sections of the 

 gills themselves, proba- 

 bly owing to its extreme 

 fineness. It is clear, 

 however, that the me- 

 dian gill receives two 

 main nerves dorso-later- 

 ally at its base, while 



Text-tig. 38. 



each lateral gill receives 

 only a single nerve 

 placed somewhat ven- 

 tral ly. As it is impossi- 

 ble to follow the changes 

 in the nervous system in such tiny organs as these gills, 1 shall 

 not mention them further, until they come plainly into view 

 in much larger gills. 



* Caudal gills of AuMroagrion cyane Selys, second instar; dorsal view; 

 ( X 90). 



t T.S. through caudal gills of Austroaf/rion cyane Selys, second instar, 

 at about one- third from base; cu, cuticle; h, hair; hm, hsemocoele; hy, hypo- 

 dermis; nit, nucleus of same; tr, trachea: ( x 37<l). 



44 



