DAHLGREN, THE MALARIA MOSQUITO 15 



when disturbed, and then only for a short time. That the larva must 

 have air in order to live makes possible its destruction by means of a film 

 of oil spread on the surface of the water. The oil, acting mechanically, 

 closes the openings in the respiratory siphon and causes the 



i i- r tv tp m • i i p Effect 



larva* to die trom suffocation. It oil is poured on the surface 



1 of Oil 



of an aquarium in which the larvae are kept, they may he seen, 



after an instant's contact with the film, in frantic contortions, as they 

 strive to free themselves from the oil, lashing the end of the abdomen 

 about and even desperately biting- the tip of the siphon. 



The last segment of the abdomen has terminally two pairs of bris- 

 tles and four elongated sac-like appendages with very thin walls, the 

 "blood-gills." On its under side it bears a large fan-like arrangement 

 of branched hairs which seems to serve as a keel or rudder. 



THE MALARIAL MOSQUITO LARVA THf COMMON WRIGGLER 



ITS USUAL POSITION IS HORIZONTAL ANO AT THE ITS USUAL POSITION 15 OBLIQUE, AND THE TIP OF THE 



SURFACE OF THE WATER. SIPHON ALONE REACHES THE WATER. 



FIG. 10. CHARACTERISTIC POSITION OF LARV/E OF MALARIA AND COMMON MOSQUITO. 



The head of the mature larva is large and rounded and is brown 

 in color. It is united to the thorax by a membranous neck 

 which allows considerable freedom of movement. Its upper larva 



surface is characteristically marked by dark-brown spots and 

 bears rows of branched hairs. On the sides of the head are the antenna' 

 extending forward, and behind these are the eyes. In front, on the under 

 side and over-hung by the elongated anterior portion of the head, is the 

 mouth, which is surrounded by a formidable armature (Fig. 9). Over- 

 hanging the mouth-parts and at the most anterior part of the head are 

 two moustache-like brushes. Below these and behind them are two 

 mandibles which move laterally and bear strong spine-like teeth for 

 crushing food. On either side of the mandibles project the cylindrical 

 maxillary palps, and below the mandibles are the flattened maxillae 

 beset with fine hairs. Below all of these mouth-parts is the small tri- 

 angular so-called "lower lip." 



