NO. 8 ANATOMICAL LIFE OF THE MOSQUITO SNODGRASS 47 



The larval head musculature appears to be largely replaced by an 

 imaginal musculature. According to Thompson (1905) there is an 

 extensive histolysis of the larval head muscles, accompanied by a 

 regeneration of muscles appropriate to the adult, which takes place 

 in the eighth to tenth hour of pupal life. 



The pupal tracheal system is weakly developed and is difficult to 

 see in dissections. According to Hurst (1890) tracheae go from the 

 base of each thoracic trumpet to various parts of the head and body, 

 and a transverse trunk connects the two trumpets. A pair of longi- 

 tudinal trunks runs back to the rear end of the body, giving off 

 branches to the internal organs and to the site of each spiracle. Only 

 the spiracles of the first abdominal segment remain open. 



In his study of the heart of Anopheles quadrimaculatus, Jones 

 (1954) reports that no evidence was found that the heart is "de- 

 stroyed, reconstructed, or otherwise drastically modified during meta- 

 morphosis." In young pupae, according to Jones, the heart beats in a 

 forward direction as in the larva, but later it may cease beating for 

 prolonged periods of time. Circulation of the blood, therefore, ap- 

 pears to be unessential for the regenerative changes taking place in 

 the pupa. 



The alimentary canal of a young pupa, as described and illustrated 

 by Hurst (1890) in Calex, might be supposed to be a functional organ 

 if the pupa could feed. It more resembles the digestive tract of the 

 larva than that of the adult, but since the adult feeds on a very dif- 

 ferent kind of food from that of the larva, the alimentary canal under- 

 goes a complete reconstruction in the pupa, details of which have been 

 described by Hurst (1890), Thompson (1905), Samtleben (1929), 

 and Richins (1938). The oesophagus is least affected insofar as its 

 epithelium goes over intact from larva to adult, but the larval pharynx 

 is lost, and an enlargement in the back of the head forms the post- 

 cerebral sucking pump of the adult. In the thorax the dorsal and 

 ventral diverticula of the adult grow out from the oesophageal wall. 

 The larval gastric caeca are absorbed and not replaced in the adult. 

 The larval epithelium of the stomach, according to Richins, de- 

 generates completely and is cast off into the stomach lumen, as a new 

 epithelium is formed by permanent regenerative cells. Transforma- 

 tion in the proctodaeum is brought about partly by histolysis and 

 histogenesis of the epithelium and partly by regrowth. The five 

 Malpighian tubules of the larva go over into the adult without change. 

 In the rectal sac of the pupa are formed six invaginations of the wall 

 that become the rectal papillae of the adult. The salivary glands of 



