i66 



Insects and Disease 



stomach they soon free themselves from the in- 

 closing sheath and make their way through the 

 walls of the stomach and enter the muscular tissue, 

 particularly the thoracic muscles. Here they un- 

 dergo a metamorphosis and increase enormously in 

 size, some attaining one-sixteenth of an inch in 

 length. 



After sixteen to twenty days they leave these 

 muscles and make their way to other parts of the 

 body. A few may be found in different parts of the 

 abdomen, but most of them make their way forward 

 into the head of the mosquito and coil themselves 

 up close to the base of the proboscis, finally finding 

 their way down into the proboscis inside the la- 

 bium. Here they lie until an opportunity offers for 

 them to escape to the warm blood of a vertebrate. 

 They probably pass through the thin membrane 

 connecting the labella with the proboscis and there 

 find their way into the wound made by the punc- 

 ture when the insect bites. Whether these para- 

 sites can gain an entrance into the circulatory 

 system in any other way is not known. It has been 

 suggested that the mosquitoes dying and disinte- 

 grating on the surface of water may liberate the 

 filariae which may later find their way into the 

 system of the vertebrate host when the water is 

 used for drinking, but most of the investigations 



