INGORGEMENT OF AIR 105 



" 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 distance through the slit in the 

 thorax. Through the ingorged air the abdomen loses its limpness, it is stiffened 

 like 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 

 anally 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." 



It appears from the observations of Eysell that the three diverticula of the 

 oesophagus perform an important function at this time, they receive the swal- 

 lowed air and it is by their means that the volume of the insect is so much in- 

 creased. During the pupal stage the diverticula contain no air whatever, but 

 immediately after ecdysis they are found inflated to the utmost. We have 

 already discussed (page 78) the double function of the large diverticulum and 

 shown that in the mature insect it serves as a food-reservoir. The two smaller 

 diverticula remain filled with air at all times. 



