142 MOSQUITOES 



tions, sucked iuto the .sttnuaclis ol* luusquitocs, lose their 

 byuliue envelope, work through the wall of the stomach 

 and enter the muscles of the thorax, where they lodg-e 

 between the muscle bundles, remaining- there for two or 

 three weeks, growing and taking on the cliaractor of the 

 larva. This is as far as the evolution was for a long time 

 observed, but upon it was based a theory by which the 

 etiology of hlariasis was explained. This was, that the 

 bodies of the mosquitoes falling in water, at death rap- 

 idly disintegrated, liberating the parasites into the water, 

 which when drunk by human beings carried the jjarasites 

 once more into the human body. 



Although plausible, it was difficult by this theory, as 

 Blanchard has pointed out, to explain the constant pres- 

 ence of the parasite in the lymphatics in the skin. How 

 can the animal introduced into the intestinal tube make 

 its way into the lymphatics of the arms and legs? It is 

 difficult to suppose that it docs this by going through the 

 lymph vessels, which are provided with valves. Bancroft, 

 of Australia, suggested that possibly the Filaria might be 

 introduced into the blood of a healthy person by the l)ite 

 of the same mosquito, assuming that the end)ryos in their 

 penetration into the muscular i^art of the thorax might 

 work into the beak. 



Through the researches of Bancroft, Manson, and Low, 

 following this idea, it was discovered that up to the sev- 

 enteenth day the larval Filarias in the mosquitoes are 

 f(mnd exclusively in the tlnn-acic muscles, but after that 

 some of them begin to travel. They collect in the con- 

 nective tissue in the anterior part of the thorax in front 



