POND LIFE. ■ 133 



be found to bear at its hinder-end a rosette of five 



platelike lobes ; this is shown at a in Fig. 109. This 



rosette can be seen imperfectly with 



a orood lens. When a larva reaches 



the surface it spreads out the rosette 



upon the surface film, which buoys it 



up in the same way that we have seen 



a needle supported by this film (see 



exneriment i, pag-e 104). The body fig. 109.— a, end of 



^ ' , 1- 1 1 1 . breathing- tube of 



of the larva is only slightly heavier larva; <^, breath- 

 than the water, and the buoyant effect ^"^ " ^° ^"^^* 

 of the surface film on the rosette is sufficient to over- 

 come this difference. 



5. Consider the adaptations in structure to the 

 mode of life of this insect : The form of the respira- 

 tory tube enables it to rest at the surface of the water, 

 where it can get a supply of air, while the greater 

 weight of the fore end of the body causes it to hang 

 down into the water in a position suited to collect- 

 ing the minute particles of decaying vegetation scat- 

 tered through the water and upon which the insect 

 feeds. This position is also one that enables the in- 

 sect to start quickly on its wriggling journey when 

 alarmed. 



6. If the student has the use of a microscope, it 

 will be well for him to make at this point a larger 

 r.nd more detailed figure of a larva than that given 

 above, which was introduced merely to show the 

 general form of these insects in this stage. 



The Pup^ of Mosquitoes {School Work).— The 

 larvae of mosquitoes develop rapidly, and after a few 

 molts change into club-shaped pupas, the head and 

 thorax being greatly enlarged in this stage. The 



