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 o-ood lens. When a larva reaches 



o 



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 



experiment i, page 104). The body - 



of the larva is only slightly heavier larva; 6, breath- 



rr ing-tube of pupa. 



than the water, and the buoyant enect 

 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.E OF MOSQUITOES (School 

 larvae of mosquitoes develop rapidly, and after a few 

 molts change into club-shaped pupae, the head and 

 thorax being greatly enlarged in this stage. The 



