2o6 ZOOLOGY FOR MEDICAL STUDENTS chap. 



thorax, its form becoming shorter and somewhat sausage-hke. Here 

 it remains for some time, growing to a length of about i-6 mm., and 

 then makes its way to the proboscis. 



Although in many cases no ill effects upon the health of the host 

 are apparent as a result of infection with Filaria bancrqfti it is believed 

 that this parasite is really the cause of those swellings of the lower parts 

 of the body known in medicine as Elephantiasis arabum. This disease 

 agrees closely in its geographical distribution with Filaria bancrqfti: 

 its direct cause appears to be obstruction of the flow of lymph and it is 

 believed that this obstruction is due to the presence of the filaria. As 

 regards the precise method by which the obstruction is brought about 

 — it is believed by some to be due to inflammatory change in the lining 

 of the lymph-spaces, brought on by the presence of the parasite, while 

 by others it is attributed to actual blocking of the lymph stream either 

 by groups of adult parasites or by their eggs. In exceptional cases the 

 female lays eggs of which the shells have not become soft and extensible 

 as happens normally, but have on the contrary remained hard and rigid. 

 Whereas the natural slender larva in its soft membranous sheath readily 

 passes through the narrow chinks of the lymphatic glands such 

 abnormal eggs retaining their ellipsoidal form are liable, on account of 

 their much greater diameter, to stick in the lymphatic gland and thus 

 obstruct the lymph-flow (Manson). 



Filaria loa 



This parasite occurs in tropical West Africa (also Uganda), living 

 preferably in the connective tissue under the skin, in which it creeps 

 actively about. Sometimes it attracts particular attention by traversing 

 the front of the eye-ball. The adult female measures about 45-60 mm. 

 in length, the male about 25-30 mm. The young are born in a sheath 

 formed by the softened egg-shell, as in the case of F. bancrqfti, and they 

 also find their way by lymph channels into the blood. They are about 

 the same size as the young of F. bancrqfti (about 250-300 ^ in length) 

 but may be distinguished by their shorter sheath and by the less regular 

 curvature of the body. They are also at once distinguishable by their 

 habits, for they migrate to the superficial vessels of the skin during the 

 daytime, on which account they were formerly usually known under the 

 name F. diurna, while the young of F. bancrqfti were known as F. noc- 

 turna. This difference in habit is due to the fact that the transmitting 

 insect is in this case not a night-flying mosquito but a biting fly of the 

 genus Ckrysops (Leiper) which is active by day. 



