342 



INTRODUCTION TO ZOOLOGY 



CHAP. 



The Larva. 



Fig. 263. — Culex pipiens. 

 Four eggs enlarged and 



From each egg emerges a small transparent 

 larva, which at once begins to swim actively 

 through the water, with the rapid contortions of body which 

 have earned it the name of "wriggler," 

 by which it is known to children. 



This larva, though able to swim so 

 rapidly, when undisturbed will remain 

 for a long time, floating motionless in 

 a vertical position, head downwards, 

 at the surface of the water (Fig. 264), 

 and its structure can then be well seen 

 with the aid of a hand lens. 



The head, thorax, and segmented 

 Werwngtiched ^^domen are all distinct, but there are 

 from them. no paired appendages at all, except on 



the head. The mouth has on either 

 side of it an appendage beset with hairs. By the constant 

 motion of these, water, with any microscopic organisms it 

 may contain, is driven into the mouth, 

 and thus food is obtained. (Compare 

 the Chameleon-fly larva, p. 336.) 

 Eespiration From the eighth segment 

 in the of the abdomen, there pro- 

 Larva, jgg^g obliquely upwards to 

 the surface of the water, a little tube 

 (Fig. 264, r), which terminates in five 

 small valves. These spread out at the 

 surface into an air-containing basin, just 

 as does the circlet of hairs of the 

 Chameleon-fly larva, and here also they 

 enable the larva to hang motionless 

 from the surface film, with its heavy 

 head downwards, taking in a fresh 

 supply of air through the spiracle at the 

 end of the tail. This spiracle is in com- 

 munication with the two great tracheae 

 of the body, which can be clearly seen 

 through the transparent skin. 



When the larva is about 



of Larva ^ ^'^ leave the surface, the valves close over the 



spiracle, and being no longer held up by the sur- 



FlG. 264.— Larva of 

 Cidex pipiens. 



r, Respiratory tube ; 

 jjj swimming organ. 



