THE ANIMAL PARASITES OF MAN 



L. loa, e.g., native children, frequently show no larvae in their blood, 

 but they may do so after years of infection. Again, in patients having 

 an infection of Mikrofilaria dinrna, there is frequently at the time no 

 evidence of the presence of Loa loa adults. Here again they may 

 appear later, but the conditions which determine whether persons 

 infected with L. loa show larvae in the blood, or persons infected 

 with Mikrofilaria diurna also show L. loa, are unknown, though 



explanations unsupported by facts 

 abound. Likewise also the mode 

 of production of the swellings is 

 unknown. 



Not uncommonly Mikrofilaria 

 perstans occurs in the blood to- 

 gether with M. diurna. 



Duration of Life. This is long, 

 as some cases have been observed 

 five to six years after leaving 

 Africa. The incubation period 

 is about a year. 



Life-history. Development of 

 the larvae takes place in the salivary 

 gl.mds of Chrysops sp. as shown 

 by Leiper. 



Geographical Distribution. 

 West Africa, especially in Congo. 



Genus. Acanthocheilonema, 



Cobbold, 1870. 



Cuticle striated longitudin- 

 ally. (Esophagus divided into 

 two portions. Tail in both sexes 

 with short lateral conical cnticular 

 appendages. Spicules unequal, 

 the larger membranous distally, 

 the smaller hooked. Vulva in 

 cesophageal region. 



FlG. 298. Acanthocheilonema perstans. 

 i, tail of male ; 2, tail showing cuticular 

 flaps devoid of fleshy contents. (After 

 Leiper.) 



Acanthocheilonema perstans, Manson, 1891. 



Syn. : Filaria perstans, P. Manson, 1891 ; Filaria sanguinis hominis var. minor, 



Manson, 1891. 



The adult female Ac. perstans measures 70 to 80 mm. in length 

 by 120 //, to 140 p in breadth. The head is club-shaped and measures 

 0-07 mm. in diameter. The vulva opens at o'6 to ro mm. from 



