OF WASHINGTON, VOLUME XIII, lull. 



the pressure from within the pupal skin bursts and the thorax 

 of the imago begins to appear through a longitudinal slit. 

 Now the imago is in direct communication with the outer air 

 and at once begins to swallow great quantities of air. Eysell 

 remarks that this can be distinctly observed by watching, 

 through the at that time unpigmented clypeus, the movements 

 of the pharynx pump. 



Hereby the volume of the mosquito is considerably increased; the 

 pupal case can no longer hold it, and, at a time when the hind end of 

 the body still remains exactly in the same position as during the pupal 

 stage, the greatly lengthened body is already forced a considerable dis- 

 tance forward through the slit in the thorax. Through the ingorged 

 air the abdomen loses its limpness, it is stiffened Hk6 an air-inflated 

 bladder, and continues to increase in volume proximally. The conical 

 form of the body thus brought about causes it to glide forward in the 

 apically narrowed pupal skin, and under normal conditions this motion 

 needs hardly any assistance from the abdominal muscles. 



The specific weight of the animal is greatly diminished by the taking 

 in of great quantities of air, a circumstance which is equally important 

 for the imago when issuing and immediately after. 



The air swallowed by the insect is, of course, taken into 

 the digestive tract. In the mosquito there are three large 

 cesophageal diverticula, concerning the function of which 

 there has been much conjecture. One of these diverticula is 

 much the largest and extends ventrally far backward into the 

 abdomen; the other two are dorsal in position. It is clear 

 from the observations of Eysell that the diverticula receive 

 the swallowed air. Christophers' already stated that the di- 

 verticula are generally found to be filled with air, although 

 he erred in the statement that they are undistended 'in the 

 newly emerged mosquito. Giles 2 was misled so far by this 

 presence of air in the diverticula that, in his discussion of the 

 anatomy of mosquitoes, he denies that they belong to the di- 

 gestive system and in consequence calls them "aspiratory 

 vesicle" and "pneumatic sacs." He defends this view at 

 some length and claims that these organs are not connected 

 with the digestive but with the tracheal system. Eysell calls 

 the two dorsal diverticula "Flugblasen" (flight-bladders) and 

 the large ventral one "Vorratsmagen" (reservoir-stomach). 

 Christophers was of the opinion that no food is taken into this 

 latter organ. 



'The Anatomy and Histology of the Adult Female Mosquito. Royal 

 Society (London), Reports to the Malaria Committee, 4th ser. , 1901. 

 2 A Handbook of the Gnats or Mosquitoes, 2d ed., 1902, pp'. 103-106. 



