POST-EMBRYONIC DEVELOPMENT OF CULEX. 183 
curved spines. These stigmata open into the air-cavity 
between the wings and beneath the thorax and first por- 
tion of the abdomen, placing this cavity in direct continuity 
with the tracheal system generally: as, however, this 
cavity is always below the surface of the water, fresh 
supplies of air cannot be taken in through it. 
From the base of the prothoracic respiratory siphons 
trachez with well-developed spirally-marked intima lead 
to all parts of the body—the most important ones being 
the two large longitudinal trunks running the whole length 
of the body. A transverse trunk runs from side to side, 
between the nerve-chain and the stomach, putting the 
cavities of the two siphons into direct communication with 
each other. To prove the continuity of the cavities of the 
siphons with that of the tracheal system generally, I re- 
moved the side-wall of the thorax from a spirit specimen, 
and having drawn out the spirit from the siphon with 
blotting paper, touched the tip with a small drop of gly- 
cerin, and I then saw the glycerin force its way into the 
siphon driving the air before it into the trachea. This I 
thought necessary because Palmén (op. cit.) has stated the 
contrary. 
In the main trunks no important change occurs after 
the beginning of pupal life. The lateral branches leading 
to the stigmata enlarge and develop a stout intima around 
the thin collapsed old one, which latter is afterwards shed. 
The fate of the soft parts of the larval siphon is much 
hike that of the larval epithelium of the stomach. The 
whole mass was introverted into the eighth segment at 
the time of escape of the pupa. During pupal life it rapidly 
disintegrates and is completely absorbed so that no trace of 
it remains at the end of the fourth day. 
The nervous system undergoes a great increase in bulk. 
At the moment of escape of the pupa the first abdominal 
