49 



specimens were found under houses, in stables, pig-pens, etc., damp 

 sites being preferred. The observations of various authors, as well 

 as those described in the present paper, all indicate that A. crucians 

 is attracted by water containing an excess of mineral salts, while 

 there is some reason to believe that a concentration of organic products 

 is equally effective. The relation of A. crucians to contaminated 

 water brings up another question that may have some important 

 bearing upon practical malaria control. Nitre cake is at present 

 used as a mosquito larvicide. This material, which is a by-product 

 of the manufacture of sulphuric acid, was one of the principal elements 

 producing the contamination of the swsmp described in the present 

 paper. It is possible, therefore, that the use of nitre cake as a larvicide, 

 far from being efficacious in that respect, may encourage the breeding 

 of A. crucians as soon as the concentration becomes low enough. 



The importance of A. crucians as a malaria carrier is being further 

 studied ; apparently it is less important than A. quadrimaculaius, 

 but perhaps more so than A. punctipennis. 



Koch (A.). Studien an Larven von Culex pipiens bei der Submersion. 



[Studies on submerged Larvae of C. pipiens.] — Zoologischer 

 Anzeiger, Leipzic, 1, no. 3-4, 6th December 1918, pp. 105-111. 



The physico-chemical mechanism of tracheal respiration in Culicid 

 larvae is not yet clear, and experiments were made with larvae of 

 C. pipiens to test the chief theories relating to the exchange of gases 

 in this process. The theories advanced by Palmen, Hertwig and 

 others, Deegener (1913) and Frankenberg (1915) are briefly summarised. 

 The observations recorded here seem to confirm Deegener's respiration 

 theory, viz., that the end-branches of the tracheae supply oxygen to 

 the organs, while the carbonic acid is taken from the blood and conveyed 

 to the larger peripheral tracheae or to the intestinal w-all and thus 

 eliminated from the body. It is however necessary to bear in mind 

 the possibility mentioned by Deegener that the carbonic acid from the 

 blood may be passed back again through the tracheae to the siphon. 

 The larvae were confined in tubes so arranged as to prevent access 

 to the surface of the water or to atmospheric air. It was found that 

 85'5 per cent, of the 131 larvae examined were heavier than water 

 and therefore sank. Gravity compensation depends on the size of 

 the larva, the degree to which the intestine is filled with food, and 

 the condition of the tracheae. The speed of passive sinking is directly 

 proportional to the size of the larva and to the quantity of food and 

 inversely proportional to the volume of air in the tracheae. The 

 tracheal system therefore plays a hydrostatic role, but the volume 

 of air contained in it depends solely on the processes of respiration. 

 When no natatory movements are made the larva sinks, assuming a 

 vertical position {Cidex position). Prolonged submersion empties the 

 tracheae and leads to a gradual change to a horizontal position 

 {Anopheles position). The j^osition of Culex larvae is therefore a 

 passive equilibrium due to the distribution of air and tissue within 

 the body. The larva seeks to re-act against the passive sinking by 

 active swimming towards the surface in quest of air. These active 

 movements gradually decrease when submersion is prolonged and 

 they finally cease. In a series of 22 experiments it was found that in 



{C546) B 



