On the Distribution of Air in the Oesophageal Diverticula and Intestine of Mosquitoes

Abstract

1. Shortly before the imago emerges, air accumulates under the pupal skin. This air is swallowed by the imago and passes directly into the stomach; the resulting distention of the abdomen helping to push the thorax forward so as to rupture the pupal skin.2. After rupture of the pupal skin, the imago continues to swallow air, which causes the stomach (and therefore the abdomen) to expand further and thereby facilitate the emergence of the imago.3. Within an hour after complete emergence of the imago, the air in the mid-gut commences to pass forward into the (hitherto empty) oesophageal diverticula, and after 12–22 hours the mid-gut no longer contains air. (Note. We find that the process of emergence here described for Culicidae also applies to some other diptera which, like mosquitoes, live for a part of their lives in water.)4. In mosquitoes fed on liquid (e.g. raisin juice) other than blood, the liquid goes direct into the oesophageal diverticula and displaces the air from them more or less completely (the experiments of Nuttall and Shipley (1903, p. 177) showed the air to be thus displaced, but this point was not specially mentioned by them).5. When mosquitoes feed on blood (whether previously fed on raisin juice or not) all the blood goes direct into the mid-gut. (Note. Traces of blood, negligible in quantity but sufficient to cause visible coloration, are occasionally to be observed in the diverticula. This appears more likely to happen in cases where no previous meal of raisin juice has been taken.)6. When a mosquito is fed on raisin juice and subsequently starved for a few days, the fluid contents of the diverticula are entirely replaced by air. The experiments indicate that this air reaches the diverticula via the cardia, in the same manner as during their initial inflation.7. In the case of “domestic” mosquitoes, the air in the diverticula becomes reduced in quantity (sometimes disappearing altogether) prior to hibernation, and increases in amount towards the end of the hibernating period.8. In the case of male mosquitoes, the transference of air from the mid-gut to the oesophageal diverticula proceeds pari passu with the turning of the hypopygium, the two processes terminating at about the same time.