case of Wuchereria bancrofti and by Harwood (1932) in the 

 ease of Litomosoides carinii. 



The microfilariae of Onchocerca, which are unsheathed, differ 

 from those of other filariae in that they live in the skin, and 

 do not enter eitlier the lymphatic or blood systems. The adult 

 worms, living in subcutaneous tissues, are encapsulated by the 

 host in hard nodules, through which the larvae are able to 

 burrow and escape. The salivary secretion of the intermediate 

 hosts (Simulium) seems to exert a definite chemotactic effect 

 on the microfilariae, since they may be many times more nu- 

 merous in the stomach of a fed fly than in a comparable quan- 

 tity of tissue. 



The intermediate hosts are usually Diptera. Fleas were 

 stated by Brein! (1921) to serve as intermediate hosts for 

 Dirofilaria immitis and Summers (1940) corroborated this, 

 showing that development would occur in several species of 

 fleas, and in a shorter time than in mosquitoes. Noe (1908) 

 followed the development of Dipetalonema (jrassH in a tick, 

 Shipicephalus sanguineus; the microfilariae of this species are 

 said to be too large to enter the blood circulation and are found 

 m the lymph, which the ticks suck more than they do blood at 

 the beginning of a meal. This work has not been confirmed 

 and is open to suspicion in view of the fact that the embryos 

 of related species {Dirofilaria reconditum, Dipetalonema per- 

 stans) live in the blood and develop in mosquitoes. Savani 

 (1933) has also reported filariae in dog ticks in areas where 

 Dirofilaria immitis is common. The intermediate hosts of 

 Wuchereria and Foleyella are various mosquitoes; of Dipeta- 

 lonema perstans and Mansonella ozzardi, Culicoides; of Loa loa. 

 Chrysops; of Onchocerca spp., Simnlium or Culicoides; and of 

 Dirofilaria, fleas and mosquitoes. 



There is some variation with respect to the site of develop- 

 ment in the intermediate hosts. The majority of the species 

 studied — Tfuchereria bancrofti, Microfilaria malayi (adult per- 

 haps unknown), Dipetalonema, Mansonella, Dirofilaria recon- 

 ditum, and Onchocerca spp. — develop in the thoracic muscles 

 of their dipteran hosts, but Loa loa develops principally in 

 the muscles or fatty connective tissue of the abdomen of Chry- 

 sops (Connal and Connal, 1922), and Dirofilaria immitis devel- 

 ops in the haemocoele of fleas and in the Malpighian tubules of 

 mosquitoes. These sites of development are of great interest 

 in view of the similar sites utilized by Draschia and Habronema 

 in museoid files. 



Fig. 195. 



Development of Wtichererm bancrofti, 1 — Larva 10 hours after in 

 fection. 2-4 — Larva 2-3 days after infection. 6-6 — Larva four days 

 and tliree hours after infection. 7-8 — Larva 5V2 days after infection. 

 1' Larva 5 M* days after infection, just before first molt. 2'-3' — Larva 

 7^ days after infection. 4' — Larva 9V2 days after infection of 

 posterior end of esopliagus. 5'-6' — Larva 11 days and 10 hours after 

 infertioa. 



290 



