LARVAL MODIFICATIONS 93 



In Uranotcenia, which is closely related to Anopheles, the closing mechanism of 

 the breathing-tube is simpler than in the more specialized larvge 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 

 tracheae 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 Uranotcenia larva 

 by short chitinous tubes which cap the trachese. 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, Aedes and other more specialized larvae 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 tracheas open and communicate with the outer air. 



The greatest specialization of the breathing apparatus is presented in the 

 larvae 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 tracheae 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 larvae there is a pair of well-developed 

 freely jointed hooks dorsally at the apex of the breathing tube. In most of the 

 culicine larvge 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 larvae of Megarhinus, Mansonia 

 and Bancroftia, and in the Sabethini ; in certain larvae 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, 



