342 



INTRODUCTION TO ZOOLOGY 



CHAP. 



The Larva. 



Four eggs enlarged and 



from them. 



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 

 FiG.2Q3.Culexpipiens. with the aid of a hand lens. 



The head, thorax, and segmented 

 abdomen are all distinct, but there are 

 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.) 

 Respiration From tfl e eighth segment 

 of the abdomen, there pro- 

 jects 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 

 Movements t leaye th gurface the va i vcs c l ose over t he 

 of Larva. . ' 



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



in the 

 Larva. 



FIG. 264. Larva of 

 Culex pipiens. 



r, Respiratory tube ; 

 p, swimming organ. 



