214 FILARIA BANCROFTI [CH. 



found on the skin in the neighbourhood of the wound caused 

 by the bite of the insect. If the skin is sufficiently moist 

 the filariae then bore their way through the epidermis into 

 the subcutaneous tissues. In some cases they may select the 

 wound caused by the mosquito as the point of entrance into 

 the body of their vertebrate host, but in most cases it is pro- 

 bable that they make an independent entrance through the 

 undamaged skin, as Looss has shewn to be the case for the larvae 

 of Agchylostoma duodenale. Moreover, Bahr has actually 

 observed the larvae of Filaria hancrofti bore into the pores of 

 the skin. The filariae were dissected out of infected mosquitoes 

 and placed in a drop of saline on the back of a man's hand. 

 The larvae could easily be seen wriggling about in the water, 

 but when placed on the skin, after a few convulsive move- 

 ments, they suddenly disappeared, apparently through the 

 orifices of the gland ducts. Six filariae were observed to 

 disappear in this manner, "with almost lightning-like rapidity." 



When the skin is very dry the young filariae often die before 

 they are able to effect an entrance, and therefore a person may 

 be bitten by an infected mosquito without developing filariasis. 

 If, however, the young worms effect an entrance, they make 

 their way to the lymphatics of their host and there develop 

 into the adult filariae. After fertilization the females then 

 develop embryos, which, on being liberated, make their way to 

 the blood circulation, and thus the life-cycle may be repeated. 



Conditions affecting the development of the filavia within the 

 body of the mosquito. One of the most important factors in- 

 fluencing development is the species of mosquito in which this 

 process takes place. In some species development occurs much 

 more readily and occupies a shorter period than in others. 

 For example, in Fiji, Bahr found that F. hancrofti developed 

 very readily in Stegomyia psetidoscutellaris, under favourable 

 conditions, the young worms appearing in the proboscis within 

 ten days. On the other hand, in Culex fatigans the develop- 

 ment proceeded much less regularly and occupied a longer 

 period, whilst in C. jepsoni and S. fasciata the worms developed 

 very slowly, and eventually degenerated in the thoracic muscles 

 without arriving at maturity. The effect of different species 



