104 TROPICAL MEDICINE AND HYGIENE 



sheath ecdysis and becomes an actively locomoting 

 larva. This larva penetrates the stomach wall of the 

 mosquito and travels to the muscular masses, usually 

 those in the thorax. When the larvae reach this shelter 

 they lie parallel to the muscular fibres and cease to be 

 actively motile, but are not encysted (fig 45). The larvae 

 swell up and become much broader ; usually a small 

 portion of the posterior extremity remains as a sharp- 

 pointed tail (figs. 43 and 44). They steadily increase in 

 size, and develop an intestinal canal, and again become 

 motile and pass into the head of the mosquito. The limit 

 of growth in the mosquito may be reached in a warm 

 climate in ten days. In cold weather and in some species 



FIG. 46. The proboscis of an infected mosquito compressed, showing the 

 filarial larvae extruded through Dutton's membrane. (From a specimen of 

 Bancroft, jun.) 



of mosquitoes this period is much prolonged. When the 

 full development of the larva is attained, it continues 

 to live for months, as long as the mosquito remains 

 alive, though no further growth takes place. 



The mature, actively motile larva travels to the anterior 

 part of the thorax or head (fig. 45), and finds its way into 

 the inferior lip or labium of the mosquito, sometimes into 

 other appendages. This part of the mouth does not 

 penetrate through the skin when the mosquito feeds, but 

 the embryos probably burst through the weak point in the 

 proboscis the membrane, Dutton's membrane, stretch- 

 ing between the two labellae (fig. 46). They do not enter 

 at the wound, but when they have escaped from the 



