LARVAL MODIFICATIONS 93 
In Uranotenia, which is closely related to Anopheles, the closing mechanism of 
the breathing-tube is simpler than in the more specialized larve and clearly 
shows the derivation of the parts. The piece within the tube is large, of irregular 
shape, and concave, the concavity towards the mouth of the tube. Its position 
in the tube is transverse. The long spur which exists in Culex for the attach- 
ment of the retractor muscles is absent, but two chitinous strips extend to the 
trachez and support them. The opposite end is bent upward and pointed, and 
against its sides the two large flaps at the rim of the tube rest. These large 
flaps are ventral in their position at the apex of the tube and represent the two 
posterior supporting plates of the Anopheles mechanism. The three remaining 
flaps represent the two lateral flaps and the anterior plate of the Anopheles larva. 
The chitinous rings of the spiracles are represented in the Uranotenia larva 
by short chitinous tubes which cap the trachee. Both orifices of these tubes are 
oblique and the upper ones are prolonged on the outer side and in contact with 
the lateral flaps which they control. 
In Culex, Aédes and other more specialized larve we find the conditions as 
described by Raschke. The triangular posterior plate of Anopheles has now 
become folded and elongated to the peculiar stirrup-shaped piece within the tube 
which is such an important component of the closing mechanism. In these 
forms the broad, hollowed out, apical portion of the stirrup closes the end of 
the tube and through it the trachee open and communicate with the outer air. 
The greatest specialization of the breathing apparatus is presented in the 
larvee of Mansonia. The tube is modified for insertion into the roots of aquatic 
plants through which the larva obtains its supply of air. The outer portion of 
the tube is greatly attenuated and furnished with serrations, while the flaps at 
the apex are transformed into a complex set of spines and hooks. With this 
apparatus the larva can pierce the plant tissues and then, by spreading the hooks, 
maintain a firm hold on the plant. The chitinous piece in the interior of the 
tube, which in large part controls the mechanism, is highly developed and ex- 
tends back through the tube into the body of the larva. 
In the Sabethini the mechanism of the breathing tube is rather simple. The 
flaps are small and the chitinous piece within the tube is reduced to a long 
slender strip. The trachex are continued as long chitinous tubes which termi- 
nate in oblique openings that face each other. The tubes are approximated 
apically and attached to the long chitinous piece. When the larva takes in air 
they are slightly protruded beyond the orifice of the breathing tube and push the 
flaps out of the way. In most sabethine larve there is a pair of well-developed 
freely jointed hooks dorsally at the apex of the breathing tube. In most of the 
culicine larvee these hooks are present but very small; they may, however, be 
well developed, as in certain species of Culex where the larva lies on the bottom 
back down and uses the hooks to maintain its position. 
The pecten of the air-tube is absent in the larve of Megarhinus, Mansonia 
and Bancroftia, and in the Sabethini; in certain larve of the latter there are a 
few spines on the tube which do not, however, appear to correspond with the 
true pecten. The other appendages of the breathing tube, hairs and hair-tufts, 
