THOMPSON: ANATOMY OF MOSQUITO. 
179 
Suddenly a crack darts across the top of the head and the pale 
pupal head shows in the gap. From two to fifteen seconds later 
the cuticle of the thorax ruptures along the mid-dorsal line and the 
respiratory trumpets spring up to the surface of the water. The 
tear in the thoracic cuticle widens and the integument of the anterior 
abdominal rings also splits along the back as the pupa rapidly works 
the head and thorax clear and wriggles forward in the compressed 
remains of the old skin, until only the apices of the mouthparts and 
legs, and the tip of the abdomen are still sheathed by it. The abdo¬ 
men is straight and each ring lies forward of its counterpart in the 
old cuticle. Hence the intima which is being withdrawn from the 
main longitudinal tracheae stretches back from the eighth segment 
to the respiratory siphon like a white cord on either side. Finally 
the tracheae are cleared, and the liberated pupa slips forward with 
flexed abdomen, rests for a few seconds, and darts away, perfectly 
formed, but of a light maltese color. The moult from the moment 
when the head cuticle splits to the clearing of the tracheal trunks 
has occupied from one minute five seconds, to one minute forty- 
five seconds. The whole process from the appearance of the air- 
sacs to the final darting away of the pupa takes on an average four 
minutes, but may occur in as short a time as two minutes or be pro¬ 
longed beyond ten minutes. 
The external aspect of the Culex pupa with its flattened head, 
high-arched thorax and nine-jointed abdomen is familiar. Male 
pupae can be distinguished from female by the larger gonapopliyses. 
The gray color of the new pupa changes in an hour or so to the 
typical black brown. A few hours before the fly emerges the pupa 
becomes quite black, owing to the formation of the imaginal scale 
pattern under the integument. Shortly after pupation a space is 
formed between the integument and the dermis of the pupa (Hurst) 
into which the scales and hairs project. This fills with air before 
the fly emerges but the imago does not become much displaced in 
relation to the parts of the pupa skin. No violent movements 
precede or accompany the liberation of the fly. The abdomen of 
the pupa straightens and the imago quietly works itself free by 
slight contractions, the emergence on the average occupying four 
or five minutes. As much more time may elapse before the 
insect takes wing. I have found in Corethra and Chironomus that 
the space between the cuticle and the dermis fills with air prior to 
