118 



of ^2 and g?_ strength a larva was observed to live 70 days ; in a ^^ 

 solution of potassium chloride a period of 57 days was observed ; in 

 a ^j solution of sodium sulphate, 37 days ; and in a gV solution of 

 potassium sulphate, 38 days on an average. 



Within certain limits the effect of the salts varies according to the 

 stages of the larvae, decreasing in the mature ones. The nitrates of 

 sodium and potassium, which are the most injurious, exercise a stronger 

 action on the two middle stages than on the last one. Magnesium 

 salts do not appear to follow any rule. The other salts, if in strong 

 solutions, act like the above nitrates ; in weak solutions their injurious 

 effect decreases and the smaller larvae are then better able to adapt 

 themselves than the larger ones. 



If the larvae were kept in a mixture of such solutions as had yielded 

 about the same average length of life, there never occurred a reduction 

 of the length of hfe, but — on the contrary — a marked increase was 

 observed in some cases, such as given by a mixture of equal parts of 

 sodium chloride \ solution and potassium chloride ^V- The develop- 

 ment of the pupae and adults was not favoured to the same degree. 

 In the presence of the salts used Chironomid larvae can stand a 4-5 

 times increase of the salt content. 



If larvae " prepared " in a given salt solution are submerged in 

 another, stronger solution of the same salt, they may be able to adapt 

 themselves, provided the solution is not one of the " fatal " group. 



The chief result of these experiments is that submersion (or even 

 " preparation ") in a solution from the " fatal " group causes an 

 accumulation of carbonic acid in the main tracheae, with, perhaps, 

 the production of gas bubbles through the stigmata. 



These results seem to lead to the following conception of the 

 mechanism of gas interchange in Culicid larvae : — Undei normal 

 conditions the tracheae obtain sufficient oxygen through the stigmata 

 and the surface of the body eliminates most of the carbonic acid 

 resulting from the changes in the cell-tissues. But it may be assumed 

 that — even normally — there exists a capacity (if only a limited one) to 

 absorb oxygen throtigh the skin and eliminate carbonic acid through the 

 tracheae. This reversed process may attain great importance under 

 abnormal conditions, such as cases in Avhich the physiological equili- 

 brium of the organism is affected by acute disturbances or by those 

 due to development. 



The collection of CO^ in the tracheae and the discharge of gas bubbles 

 through the stigmata can therefore scarcely be looked upon as a 

 sign of general degeneration of the larva ; it is not a pathological 

 character but a response to certain conditions. 



Koch (A.). Zur Physiologie des Tracheensystems der Larven von 



Mochlonyx (Lw.). — Mitt. Zool. Inst, der Westfdlischen Wilhelms- 



Universitdt, Munstcr i. W., no. 1, 20th November 1918, pp. 11-13. 



[Received 12th April 1920.] 



The results obtained with Culex larvae [see preceding paper] have 



led to experiments with other mosquitos and it was found that the 



larvae of Mochlonyx possess to even a greater degree than those of 



Culex the ability to absorb oxygen through the surface of the body and 



to eliminate carbonic acid through the tracheal system. This is easily 



explained by the biology of these species. 



