212 THE ROUND WORMS. 



head is club-shaped. The sheathed embryos are supposed to be 

 born viviparously and Manson supposes that as a result of injury to the 

 parent worm and resulting extrusion of eggs, that the blocking of lymph 

 channels occurs. These embryos show a nocturnal periodicity. Dur- 

 ing the day they remain in the lungs. The disease is transmitted 

 especially by Culex fatigans. The sheathed embryos, getting into 

 stomach of mosquito, wriggle out of the sheath, they then bore their 

 way through walls of stomach and enter into a sort of passive stage, 

 during which further development takes place. They finally become 

 distributed in the muscles of the thorax and make their way along the 

 fleshy labium, to enter the wound in a person bitten by a mosquito, by 

 way of Button's membrane. 



Filaria perstans. The adults are found in connective tissue and 

 deeper fat, especially about the mesentery and abdominal aorta. 



The female is about 3 inches long; the male is rarely found and is 

 less than 2 inches long. These worms are characterized by incurved 

 tails, the extremity of which has two triangular appendages giving a 

 bifid appearance. The embryos do not possess a sheath and have a 

 blunt tail. The life history is unknown. Both mosquito and tick 

 have been incriminated. The embryos are always present in the 

 peripheral circulation hence perstans. There does not seem to be 

 any symptomatology. 



Filaria demarquayi. The habitat of this filarial worm is the 

 West Indies. The embryo has no sheath and has a sharp tail. Other 

 filarial species which have been reported are F. magalhaesi, F. ozzardi, 

 F. volvulus, F. powelli and F. philippinensis. A species called F. gigas 

 is now considered to have been only the hair of the leg of a fly. The 

 embryos have usually been given such names as F. nocturna, F. diurna, 

 etc. Of course the embryos and the parent should have the same name. 

 It has been proposed to designate these embryos the same as the parent, 

 but with the use of the term Microfilaria instead of Filaria. 



The points usually noted in the description of filarial embryos are : 



1. Presence or absence of periodicity of embryos in peripheral 

 circulation. 



2. Presence or absence of a sac sheath around the embryo. 



