2o6 NATURAL HISTORY OF AQUATIC INSECTS CH. 



no bigger than a pin's head this bubble dilated con- 

 siderably, then contracted, and then dilated again, as 

 if air had been forced out of the tracheal tubes and 

 sucked up again. 



I have also to thank ]\Ir. J. J. Wilkinson for the 

 following account of the very peculiar phar)mx of 

 the Eristalis larva, based upon his long-continued 

 observations and inquiries. A slighter description of 

 the organ has been published by Batelli.^ 



" The head of the Eristalis larva is soft and capable 

 of changing its shape. It is rounded in front, and 

 when extended, shows two small sensory papillae, 

 which are carried on the under side. Behind these 

 is the opening of the mouth. The phar3'nx is lodged 

 in a brown chitinous capsule, below which can some- 











^''Vjj^^x 



:i:.^^X-_^-vS«^^S 



Fig. 74. — Head of larva of Eristalis, ventral view, showing mouth and sensory 



papillae. 



times be seen a fleshy process which resembles the 



tongue of the larva. The larva often puckers up its 



mouth, so as to conceal its jointed appendages, and 



^ Bill/. Soc. Ento»i. I/al., 1S79, pp. 77-120, pi. 1-5. 



