442 



ANIMAL RESPIRATION 



body, with which are connected the only breathing-pores devel- 

 oped. For instance, the larva of the Drone- Fly {Eidstalis tenax) 

 is commonly known as the "rat-tailed maggot", on account of 

 its possessing such a tube at the hinder end of the body (fig. 559). 

 Special provision for a supply of air is particularly necessary in 

 a form like this, for it lives in liquid filth, and so can only be called 

 " aquatic " by courtesy. 



The larvae of the Common Gnat {Culex pipiens) are little red 

 wriggling creatures, abundant in stagnant water. Each of them 



has a breathing-tube near the end of 

 its tail, and every now and then comes 

 to the surface for air, at which times 

 the tip of the tube is pushed above 

 the surface, and its valvular aperture 

 opened. The valve is again closed 

 when the larva has taken in sufficient 

 air for the time being. Later on the 

 quiescent pupa-stage in the life-history 

 is reached, during which the creature 

 floats at the top of the water, breath- 

 ing now by means of a couple of tubes 

 which project from the first ring of the 

 thorax, the larval tube having disappeared. The pupa, however, 

 is not so completely passive as the corresponding stage in a beetle 

 or butterfly, for it is able to dive if necessary to escape any danger 

 which threatens (fig. 560). 



Fig. 560. — Larva (on left) and Pnpa (on right) 

 of Common Gnat [CuUx pLpie^is), enlarged 



SCORPIONS, SPIDERS, AND MITES (Arachnida) 

 AS AIR-BREATHERS 



Upon the under side of the broad part of a Scorpion's abdomen 

 four pairs of oblique slits are to be seen, opening into complex 

 lung-books, which have been compared to plate-like appendages 

 found in the corresponding region of a King- Crab. The air- 

 containing cavity of each of these structures is largely filled by 

 a considerable number of thin plates, which project inwards almost 

 like the leaves of a book. The plates contain numerous blood- 

 spaces, and collectively present a very large breathing-surface. It 

 will be seen that the breathing organs are much more localized 

 than those of the air-breathing arthropods already described, and 



