268 THE ROUND WORMS 



The sexes are usually found together. The females are about 3 inches long 

 and the males less than 2 inches. The tails of both sexes are incurved, but that 

 of the male is more so. The head is club-shaped. The vulva opens 1.2 mm. from 

 the anterior end. There are 2 uterine tubules. 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, the blocking of lymph channels occurs. 



A very interesting fact is that people with elephantiasis fail to show larvae in the 

 peripheral circulation. Manson considers that it is due to the blocking of the lymph 

 channels. 



These embryos show a nocturnal periodicity. During the day they 

 remain in the lungs, and larger arteries. 



If the patient sleeps in the day time and is active at night the nocturnal perio- 

 dicity or presence of embryos in peripheral circulation is inverted. In the case of 

 F. loa, however, a change of habits does not change the periodicity of the filarial 

 embryos, they continue to appear in the peripheral circulation by day even if the 

 patient sleeps at that time. 



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. This takes about 

 twenty days at which time the larvae are about 1/16 inch long and have an alimentary 

 canal. 



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 (75 mm.) 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 symp- 

 tomatology. 



It is of historical interest that F. perstans was once considered the cause of 

 sleeping sickness. 



Filaria volvulus. This is a rather common parasite of Central Africa. The 

 male is about 11/2 inches (35 mm.) and the female about 5 inches long. The 

 females are so interlaced in the fibro-cystic swellings that it is difficult to determine 

 their length. The tumors start from the presence of a worm in a lymphatic. The 

 tumors are easily enucleated. Adults are striated. They are found in cystic tumors, 

 especially about the axilla and popliteal space. The cystic contents contain abundant 

 sheathless larvae about 300/4 long; they are not found in the peripheral circulation. 

 Life history unknown, although it has been suggested that a species of Glossina 

 may be concerned. 



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 



