68 BIOLOGY OF ADULT MOSQUITO [CH. 



After piercing the skin the insect begins to pass its sahvary 

 secretion along the groove in the labrum. The function of 

 this secretion is, however, quite unknown. Meanwhile the 

 amount of carbon dioxide in the tracheae of the insect increases 

 considerably owing to its proximity to the body of its host 

 and as a result the muscular contractions are considerably 

 augmented. The effect of this increase in the muscular con- 

 tractions is to cause compression of the oesophageal diverticula, 

 and their contents, consisting of bubbles of carbon dioxide 

 and also of a fungus, are forced into the oesophagus and for- 

 wards through the proboscis into the wound caused by the 

 bite. The lumen of the proboscis, buccal cavity and oeso- 

 phagus is thus filled with carbon dioxide, derived from the 

 diverticula, and this gas is supposed to retard the coagulation 

 of the blood. The fungus, which is also extruded from the 

 diverticula, enters the skin and is the cause of the great irritation 

 and local swelling that often follow the bite of a mosquito. 

 The association of this fungus with the mosquito constitutes 

 one of the most interesting cases of commensalism hitherto 

 described. The fungus is present in the egg, larva and pupa, 

 and can always be found in the oesophageal diverticula of 

 freshly emerged mosquitoes. In this region it multiplies on 

 the food which is taken into the diverticula, and during its 

 growth produces bubbles of carbon dioxide. When the mos- 

 quito feeds, the majority of the fungi and the bubbles of 

 carbon dioxide are extruded, but the few remaining fungi 

 rapidly grow on the blood which passes into the diverticula 

 during the meal, and thus more carbon dioxide is produced. 

 Schaudinn shewed that the inoculation of the salivary glands 

 of the mosquito into the skin did not produce any effect, 

 whereas the inoculation of the contents of the ventral diverti- 

 culum was followed by the formation of an irritant swelling 

 resembling that caused by the bite of a mosquito. These 

 results have also been confirmed by Major Williams, LM.S., 

 whilst working in the Quick Laboratory, Cambridge. 



Colour. Mosquitoes, like all other blood-sucking insects, 

 have a decided preference for dark colours and avoid lighter 

 shades. Nuttall found that dark blue and dark red were the 



