28 THE BOOK OF NATURE STUDY 



apparatus which necessitates life at the surface in quest of the 

 atmospheric oxygen itself. 



Towards the end of larval life the prothorax becomes dis- 

 tended, and the appendages of the future gnat can be faintly 

 discerned through the skin. The pupa itself lies in the mud or 

 slime, allowing only the head and thorax to project above its 

 level. From the top of the prothorax dense tufts of respiratory 

 filaments stand out into the water, and these are kept constantly 

 moving by gentle swaying of the body. The hind end of the 

 body has a paired tail-fin margined with long bristles for the 

 purpose of locomotion. As in the pupa of culex, eyes, antennae, 

 wings and legs are present, and contain the corresponding organs 

 of the imago pressed down against the sides and ventral surface 

 of the throax, but are incapable of movement. At this stage 

 the colour of the blood becomes a deeper red. Soon after the 

 commencement of pupal life the system of tracheal tubes be- 

 comes strongly developed and filled with gas ; so that before 

 long the pupa is floated up to the surface ready for the emerg- 

 ence of the imago. At length the gas passes out through the 

 spiracles on the side of the imprisoned imago into the space be- 

 tween the skin of the imago and that of the pupa. The pupal 

 skin is thus distended until at last it bursts. Instantly the imago 

 steps out, rests a moment upon the floating husk, and then flies 

 away. The emergence is extraordinarily rapid. 



BIBLIOGRAPHY. Miall, Natural History of Aquatic Insects and Trans. Entom. 

 Soc., 1893 ; Miall and Hammond, Trans. Linn. Soc., vol. v., 1892 ; Hurst, " The 

 Pupal Stage of Culex," Studies from the Biological Laboratory of Owens College, 

 vol. ii., 1890 ; Hurst, " Life-History of a Gnat," Trans. Manchester Micr. Soc., 

 1890. 



