THE PUPA. 



The pupa of mosquitoes, like the larva, is aquatic, but depending upon 

 communication with the air for respiration. The pupa is active and capable of 

 moving rapidly through the water but it takes no food, the appendages of the 

 head and thorax of the future fly being enclosed in a common chitinous covering. 



The appearance of the pupa differs greatly from the larva. The anterior 

 portion is large and very robust and composed of the head and thorax enclosed 

 in a common casing, in which, however, the component parts, the head with its 

 appendages, and the three segments of the thorax with their appendages, can 

 be distinguished. The head, wings and legs are packed together ventrally and 

 laterally, so that in a dorsal view only the dorsum of the thorax is visible. The 

 abdomen consists of nine flattened segments, freely movable, of which the first 

 eight are roughly quadrate in outline and slightly broadened posteriorly. The 

 eighth segment bears at its apex a pair of large chitinous plates, the " paddles " 

 or " fins." 



Eespiration in the pupa takes place through a pair of appendages on the 

 thorax, the " respiratory trumpets " or " horns." The respiratory trumpets 

 are inserted at their bases on the mesothorax, anteriorly to the bases of the 

 wings, and communicate with the anterior pair of thoracic spiracles. When 

 the pupa is at the surface of the water the trumpets break through the surface 

 film and admit the air to their interior and into the tracheae. 



When the pupa is at rest at the surface of the water the dorso-ventrally 

 flattened abdomen is curved under the bulky cephalo-thorax and almost in con- 

 tact with its ventral surface. In this attitude the " paddles," which are terminal 

 in position, point directly forward. By lashing with its abdomen the pupa can 

 descend rapidly into the water. Owing to the fact that the specific gravity of 

 the pupa is less than the medium containing it, the pupa is rapidly carried to 

 the surface as soon as it ceases its efforts. It should be noted that the specific 

 g^a^dty of the pupa differs with age, the pupa becoming lighter as it approaches 

 maturity. There is also considerable difference according to species, the pupge 

 of some being so nearly of equal specific gravity with the water that they can 

 remain nearly stationary at the bottom or at a certain depth. Certain pupae, 

 when alarmed, can remain below for some time by clasping objects with the 

 abdomen. 



The pupa is very easily alarmed and at the appearance of a shadow, or at a 

 slight disturbance of the water, it immediately darts towards the bottom. 

 Hurst has found that the cephalo-thorax of the pupa contains a large air-cavity, 

 which must be very effective in lightening it and in maintaining its equilibrium. 

 The pupa is additionally lightened towards the period of eclosion by the secre- 

 tion of air beneath the pupal skin, as will be described in connection with the 

 emergence of the imago. Hurst describes the cavity just referred to as follows : 



8 99 



