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.” 
Respiration 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 trachex. 
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 
gravity of the pupa differs with age, the pupa becoming lighter as it approaches 
maturity. There is also considerable difference according to species, the pupe 
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 pupe, 
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: 
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