25 
siphon reaches the surface, fresh air flows into its trachez, and the phys- 
ical properties of the so-called surface film of the water assist it in 
maintaining its position. 
The respiratory tube takes its origin from the tip of the eighth ab- 
dominal segment, and the very large trachez can be seen extending to 
its extremity, where they have a double orifice. The ninth segment of 
the abdomen is armed at the tip with four flaps and six hairs, as shown 
in fig. 8. These flaps are gill-like in appearance, though they are prob- 
ably simply locomotory in function. Withso remarkably developed an 
apparatus for direct air breathing there is no necessity for gill struct- 
ures. Raschke’ and Hurst” consider that the larva breathes both by 
the anus and by these gill flaps, as well as by the large trachee which 
open at the tip of the respiratory tube. Raschke considers that these 
trachee are so unnecessarily large that they possess a hydrostatic 
function. The writer is inclined to believe that the gill flaps may be 
functional as branchial structures in the young larva, but that they 
largely lose this office in later life. 
After seven or eight days, at a minimum, as just stated, the larva 
transforms to pupa. The pupa, as has been repeatedly pointed out 
with other species, differs most pronouncedly from the larva in the 
ereat swelling of the thoracic segments. In this stage the insect is 
lighter than water. It remains motionless at the surface, and when 
disturbed does not sink without effort, as does the larva, but is only 
able to descend by a violent muscular action. It wriggles and swims 
as actively as does the larva, and soon reaches the bottom of the jar 
or breeding place. As soon as it ceases to exert itself, however, it 
floats gradually up to the surface of the water again. The fact, how- 
ever, that the larva, after it is once below the surface of the water, sinks 
rather than rises, accounts for the death of many individuals. If they 
become sick or weak, or for any reason are unable to exert sufficient 
muscular force to wriggle to the surface at frequent intervals, they will 
actually drown, and the writer has seen many of them die in this way. 
It seems almost like a contradiction in terms to speak of an aquatic 
insect drowning, but this is a frequent cause of mortality among wrig- 
glers. This fact also explains the efficacy of the remedial treatment 
which causes the surface of the water to become covered with a film of 
oil of any kind. Aside from the actual insecticide effect of the oil, the 
larvee drown from not being able to reach the air. Thestructure of the 
pupa differs in no material respect from that of corresponding stages 
of European species, as so admirably figured and described by the older 
writers, notably Réaumur and Swammerdam’, and needs no description 
?Raschke, Die Larve von Culex nemorosus, Berlin, 1887. 
* Hurst, the Pupal Stage of Culex, Manchester, 1890. 
* Even Bonanni, in 1691, gave very fair figures of the larva and pupa of a European 
species. Micrographia Curiosa, Rome, MDCXCI, Pars. II, Tab. I. 
