56 



was used and the effects compared with those of kerosene and paraffin, 

 with the result that it seemed to have the same action as paraffin, but 

 acted differently from kerosene, which tends to prove that the action 

 of this last is not due to a mechanical blocking of the siphon tracheae, 

 for their effect in this respect should be similar. 



Since the difference between the time of survival under kerosene and 

 paraffin was so inconsiderable, it was suggested that the larvae had 

 escaped the poisonous action and had succumbed mainly as the result 

 of being prevented from breathing the external air. Observations 

 were therefore made on the oxygen requirements of submerged mos- 

 quito larvae. Certain factors had to be considered when carrying out 

 these observations. The species of mosquito is of primary importance, 

 e.g., S.fasciata has apparently a higher power of resistance than either 

 C. fatigans or C. invidiosus. It is pointed out that the relation of the 

 basal diameter to the length of the siphon is in the case of C. invidiosus 

 1 : 8, in C. fatigans 1 : 4, and in S. fasciaia 1 : 2, and that according to 

 Sen the power of S. fasciata to withstand the want of oxygen better 

 than Culex apparently has a natural connection with the respective 

 lengths of their respiratory siphons. The age of the larvae is important, 

 as young larvae were found to survive longer than fully developed ones. 

 The temperature is another factor, for it was found that a lowering of 

 temperature prolonged and a raising of it shortened the period of 

 survival of submerged S. fasciata larvae. The presence of organic 

 matter in the medium also profoundly modifies the power of survival of 

 larvae submerged in it. This undoubtedly shortens the period during 

 which mosquito larvae can survive when submerged in a fluid, since it 

 absorbs and uses up the dissolved oxygen. Experiments also go to 

 prove that the presence of organic matter is comparable to the effect 

 produced on larvae submerged in water from which the oxygen has 

 been expelled by boiling. In one experiment with S. fasciata larvae 

 the presence of water weed in the medium appeared to prolong the life 

 of the insect, a certain amount of oxygen being given off by it. 



From the above experiments, it is deduced that the larvae died in 

 consequence of the reduction from various circumstances of the 

 dissolved oxygen to an amoimt that ceased to be of use for cutaneous 

 respiration. Experiments were therefore made in order to determine 

 the part played by cutaneous respiration, and the proportion of dissolved 

 oxygen available for this process had to be considered. The experi- 

 ments dealing with this point could not be satisfactorily carried out 

 with the apparatus available and no definite data were therefore 

 obtained, but yoimg larvae were found to adapt themselves more 

 easily than older ones, and though not surviving as long as they 

 theoretically might have done, they nevertheless lived for many days, 

 grew in size, moulted and developed fully. Experiments are described 

 which deal with the survival of mosquito larvae submerged in slowly 

 ru n ning water, being an attempt to reproduce more nearly the con- 

 ditions present in a pool or stream in which the water is not held fast 

 until its oxygen is exhausted, but is able to circulate more or less freely. 

 These experiments confirm those carried out by A. da Costa Lima [see 

 this Review, Ser. B, ii, p. 107] and show that the larvae of certain species 

 of mosquitos, including S.fasciata, are undoubtedly capable of adapting 

 themselves to a submerged life, and in this state continue to develop 

 up to the point at which pupation would naturally take place. This is 



