198 



3. The filament is very short, a mere spike-like 

 process. 



N. Stephens! 



N. maculatus 



N. theobaldi j 



N. maculipal-pis 



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, (i) 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 -y8 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- 1 02 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. 



