1*512 J. AV. SCOTT MACFIK. 



nu'tliocl eni[)l()V(Ml hy mo was not (>])on to any of these ol)jeftions, and yet I am able 

 to coniirm the statement t)iat Sen regards as so remavkable, namely, that young larvae 

 without any tree air " t,'row and may even become nymphae." 



The laivae of certain species of moscjuitos, including Stiyotnyia fasciata, are un- 

 doubtedly capable of adapting themselves to a submerged life, and in this state con- 

 tinue to develop u]) to the point at which pupation woidd naturally take ])lace. 

 Pupation, however, is usually delayed, but if it does occur, the mosquitos die, since 

 the pupae are unal)le to survive without direct access to free air. The practical 

 bearing of tliis ])heiu)menon would seem to be that it indicates one way in which 

 moscjuito larvae may escape the action of injurious substances applied to the surface 

 of pools to kill theuK and may explain why it is that " oiling" iu practice is less 

 successful than theoretically it should be. Many species of mosquito larvae spend a 

 considerable part of their time at the bottom, and if on rising to breathe they are 

 disturbed or find the surface unsatisfactory they often sink dowai to the nuid and 

 rejuain for a longer or shorter time in a (juiescent condition. The majority of the 

 larvae no doubt would be killed as a result of coming into contact with the oil, but 

 some might escape, and the experiments recorded above prove that they would be 

 capable, if necessary, of prolonging their submerged existence for a period long enough 

 to allow the most liberal application of kerosene to evaporate. 



The Results of "Oiling" with Crude Kerosene as observed in Laboratory 

 Experiments. 



Returning now to tJie question of the efficiency and general applicability of oiling, 

 it may be of interest to record the results observed wdien crude kerosene was applied 

 to fluids in which various species of mosqiuto larvae were living. 



Anopheles eo-slalis. The larvae of A. roshills do not survive for long the effects of 

 oiling. In one experiment four larvae were placed in a jar containing a layer of tap- 

 \vater 8 cm. deep. To the surface of the water, which measured 5 cm. by Idem., 

 kerosene was added in a proportion etpial to 10 cc. per s(|uare metre and the water 

 agitated. Half an hour later the larvae were moribund, and in one hour they were 

 ail dead. 



If the amount of kerosene added was more than enough to form a mere film, the 

 larvae were apt to get caught by it when they came to the surface, and were apparently 

 unable to free themselves. In these circumstances they lay on the surface wriggling 

 feebly until they died, and the oil tended to collect in a thicker layer round theii- 

 bodies. 



Cule.r falujans. The larvae of C.fatigans in laboratory experiments are also killed 

 rapidly by the application of Icerosene to the surface of the fluid in which they are 

 living. In one experiment a single small drop of crude kerosene was added to each 

 of nine small tubes of Huid 1"5 cm. in diameter in each of w'hich a single fully developed 

 (\ faligaiis was living. Eight of the larvae w'cre found dead after half an hour, and 

 the ninth after an hour. 



The details have already been given (see p. D) of another experiment witli this 

 species showing that the action of the kerosene on the larvae is a direct one and is not 

 dependent on the solution of part of the oil by the fluid to which it is a])plied. 



