NO. 8 ANATOMICAL LIFE OF THE MOSQUITO — SNODGRASS 3 1 



the general integument of the larva as well as by the anal lobes. The 

 submerged mosquito larva, therefore, breathes through its skin, and 

 some other aquatic larvae are known to do the same. 



From experimental ligaturing of the body of the larva in different 

 places, Wigglesworth furthermore showed that the larva absorbs 

 water from the posterior end of the body, presumably through the 

 thin, permeable anal lobes. During feeding, the larva does not swallow 

 the water taken into the pharynx with its food, this water, as already 

 noted, being discharged from the mouth. The anal lobes thus serve 

 to maintain the physiological balance of water in the larval body. 



INTERNAL ANATOMY 



Inasmuch as the principal specializations of the mosquito larva have 

 to do with feeding and breathing, there is little in the internal or- 

 ganization that is essentially different from that of other insects. 



The tracheal system. — The tracheal system of most insects in- 

 cludes a pair of lateral tracheal trunks running lengthwise through 

 the body, with which the lateral spiracles are connected. Many insects, 

 however, have also a pair of dorsal longitudinal trunks. In dipterous 

 larvae, including the mosquito larva, that breathe through dorsal 

 spiracles, the dorsal trunks are particularly large (fig. 10 A, dTra), 

 and the lateral trunks connected with the closed lateral spiracles 

 are much reduced. The dorsal spiracles of the ninth abdominal 

 segment are evidently secondary respiratory apertures to allow the 

 larva to breathe at the surface of the water, since it is hardly to be sup- 

 posed that a primitive lateral spiracle could migrate dorsally and 

 change its tracheal connections. In general the last pair of lateral 

 spiracles is on the eighth segment. In the larvae of higher Diptera 

 there is also a pair of secondary anterior dorsal spiracles on the thorax. 



The fine end branches of the insect tracheal system in general go to 

 the cells of the body tissues, which are thus directly oxygenated. In 

 the larva of Anopheles, Imms (1907) describes a series of small tubes 

 from the longitudinal trunks in the eighth abdominal segment that 

 break up into fine branches going to the posterior end of the heart. 

 Imms suggested that these branches may oxygenate the blood in the 

 heart, but Jones (1954) says they end on the heart wall. 



At each larval ecdysis the cuticular intima of the tracheal tubes is 

 shed with the outer cuticle. In the mosquito larva, according to Wig- 

 glesworth (1949), the intima of the main tracheal trunks breaks be- 

 tween the segments, and the pieces attached to the shed cuticle are 

 drawn out through the lateral and the posterior dorsal spiracles of 



