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are devoured, if at all. The carnivorous forms 

 Nepa, Corysca, Libellula rapidly devour larvae. 

 Hydrophilidae beetles, tadpoles, etc., do not destroy 

 larvae. Observe that some species of fish are 

 much more active devourers of larvae than others. 

 Note that weeds often protect larvae from being 

 consumed by small fish. 



8. Make experiments with different chemical 

 and other bodies, and note the absence or presence 

 of culicidal power. 



(a) Note that chemical bodies in solution kill 

 only with difficulty, as a rule, e.g., corrosive sub- 

 limate. Ammonia, however (i in 4,000 of water) 

 will kill mature larvae according to Waddei.l. 



(h) Note that oils rapidly kill larvae by blocking 

 the air tubes. Treat larvae by pouring a little 

 olive oil upon the water. Stain with osmic acid 

 and note globules of oil within the air tubes. 



9. Add some paraffin oil to a smsill Anopheline 

 pool, observe the presence next morning of dead 

 female mosquitoes that have come to lay their 

 eggs. Observe the effect of paraffin on different 

 kinds of natural water, and the great efficacy in 

 some cases and futility in others. 



10. Observe that pools covered with Lemna 

 are very frequently, if not always, free from 

 larvae. The action of the Lemna is said to be 

 mechanical. 



Examination of other Larvae 



Dixa. — In its movement along the surface 

 of the water the larva of Dtxa resembles Anopheline 

 larvae, and this larva also rests horizontally just 

 beneath the surface film. 



