POST-EMBRYONIC DEVELOPMENT OF CULEX. 185 
cuticle just behind the first abdominal tergum. The distal 
side of the plate divides into a few setee, which by repeated 
branching give rise to about one hundred straight setze all 
lying in one plane parallel to the median axis of the body, 
and each bearing a few fine hairs. They are shown dia- 
grammatically in fig. 1. When the pupa is at rest the 
tips of the setze are just at the surface of the water. 
Hach antenna of the male imago consists of three por- 
tions. The swollen basal joint, a series of twelve joints 
bearing long hairs, and a terminal portion consisting of two 
long joints with only small hairs. A. M. Mayer (5) has 
shown by experiments upon mosquitos that when a tuning 
fork of a certain note (Ut, = 512 vibrations per second) 
was sounded these hairs were set in violent vibration, 
especially when the sound came in the direction of the 
axis of the antenna. ‘This note corresponds pretty closely 
with the chief note produced by a special vocal organ on 
each side of the thorax of the female—not the ‘‘ buzz”’ of 
the wings but a much higher note, and the antenna has 
therefore been regarded as an organ of hearing. The 
structure of the basal joint or “‘ ear”? supports this view, 
for it appears to be specially adapted for perceiving 
longitudinal vibrations of the shaft. 
The ‘‘ ear”’ is a nearly hemispherical cup with very thick 
walls which are turned in at the edge, the turning-in going 
so far in the male that the inturned portion reaches the 
floor of the cup and becomes closely applied toit. The 
strong chitinous covering of the rest of the body covers 
the whole surface of the cup and the shaft, but it is thinner 
on the inner than on the outer surface of the cup. The 
shaft is attached rigidly to the floor of the cup, and a 
series of radiating thickenings run in the floor from the 
base of the shaft outwards. A longitudinal vibration of 
the shaft would thus cause this plate to vibrate. 
