9 8 
3. The filament is very short, a mere spike-like 
process. 
N. stephensi 
N. maculatus 
N. theobaldi 
N. maculipalpis 
10. The Stigmatic Syphon. —The eighth segment 
bears the stigmatic opening. This is a large quadri¬ 
lateral space, with comb-like chitinous processes on 
either side. These differ in different species, and are 
of much importance in classification. 
The ninth segment is cylindrical in shape, and 
is chiefly notable from the fact that it carries four 
large transparent papillae well supplied with air tubes 
and certain long curved hairs. Of the hairs, one series 
projects downwards so as to resemble a rudder. The 
others project posteriorly. There does not appear 
to be much variation in the different species. 
Duration of Larval Stage. —‘This is determined by at least two 
factors. (1) Food. —Thus larvae kept in tap-water in the laboratory 
grow very slowly, if at all. (2) Temperature. —Thus the larval stage of 
A. maculipennis varies from sixteen to twenty-two days at air tempera¬ 
tures of 68°-78° F., while in the tropics the time is much shorter, 
e.g., twelve days for Ce. Argyrotarsis in Havana, and eleven days for 
M. rossi, where the temperature of the water varied from 96 °-io2° F. 
Pupation 
Just before this process the larva becomes quieter. 
The attitude also frequently alters, becoming a hanging 
one, somewhat like that of a Culicine larva. 
In this condition larvae are very readily killed 
by agitating the water (and it is difficult to carry 
larvae in this stage without killing them). 
The change into the nymph is very sudden. A 
few rapid motions and the larval skin is cast off, leaving 
the characteristic nymph. 
