178 Arthropods as Essential Hosts of Pathogenic Organisms 
Several other cestode parasites of domestic animals are believed 
to develop their intermediate stage in certain arthropods. Among 
these may be mentioned: 
Choanotcenia infundibulformis,oi chickens, developing in the house¬ 
fly (Grassi and Rovelli); 
Davainea cesticilhis, of chickens, in some lepidopter or coleopter 
(Grassi and Rovelli); 
Hymenolepis anatina, H. gracilis, H. sinuosa, H. coronula and 
Fimbriaria fasciolaris, all occurring in ducks, have been reported as 
developing in small aquatic crustaceans. In these cases, cysticer- 
coids have been found which, on account of superficial characters, 
have been regarded as belonging to the several species, but direct 
experimental evidence is scant. 
Arthropods as Intermediate Hosts of Nematode Worms 
Filariasis and Mosquitoes— A number of species of Nematode 
worms belonging to the genus Filaria, infest man and other verte¬ 
brates and in the larval condition are to be found in the blood. 
Such infestation is known as filariasis. The sexually mature worms 
are to be found in the blood, the lymphatics, the mesentery and sub¬ 
cutaneous connective tissue. In the cases best studied it has been 
found that the larval forms are taken up by mosquitoes and undergo 
a transformation before they can attain maturity in man. 
The larva; circulating in the blood are conveniently designated 
as microfilariae. In this stage they are harmless and only one species, 
Filaria bancrofti, appears to be of any great pathological significance 
at any stage. 
Filaria bancrofti in its adult state, lives in the lymphatics of man. 
Though often causing no injury it has been clearly established that 
they and their eggs may cause various disorders due to stoppage 
of the lymphatic trunks (fig. 119). Manson lists among other effects, 
abscess, varicose groin glands, lymph scrotum, chyluria, and ele¬ 
phantiasis. 
The geographical distribution of this parasite is usually given as 
coextensive with that of elephantiasis, but it is by no means certain 
that it is the only cause of this disease and so actual findings of the 
parasites arc necessary. Manson reports that it is “an indigenous 
parasite in almost every country throughout the tropical and sub¬ 
tropical world, as far north as Spain in Europe and Charlestown in 
