METAMORPHOSIS OF FILARIA BANCROFTI, COBB. 55 



this only occurs when the worm is swimming tail first ; such 

 appearance cannot be seen in every embryo, and I am inclined to 

 think that it is not normal (Fig. 2). The flagellum-like body is 

 the collapsed sheath, which can only be diagnosed as a sheath 

 when endosmosis has taken place. Those who have figured the 

 embryo, have represented a worm inside a distended sack; such 

 appearance is unnatural. The purpose of the sheath is possibly 

 to anchor the worm to the side of a blood vessel when the latter 

 is resting. 



Manson in his recent work 1 p. 460, has remarked : — " It is also 

 manifest that the purpose of the "sheath" with which it is pro- 

 vided while circulating in the human host, is to muzzle the embryo 

 filaria and prevent its breaking through the blood-vessels, and so 

 missing its chance of gaining access to the mosquito." 



If any should care to decide the question for himself, let him 

 prepare a slide of filariated blood and paint a little oil round the 

 edge of the cover-glass to prevent evaporation and examine under 

 the microscope twenty four hours afterwards, when a certain 

 amount of coagulation and crystallisation has taken place ; this 

 forms some resistance to the filarise and they may be seen crossing 

 from one edge of the cover-glass to the other in a tortuous but 

 definite course with the collapsed sheath following tail. 



I cannot agree with Manson that the sheath muzzles or impedes 

 the filaria in any way; normally I believe the sheath is never 

 separate from the body. The embryo in freshly drawn blood 

 wriggles about but never seems to leave the same spot ; this 

 peculiarity was considered due to some impediment caused by the 

 sheath, but the embryo of Filaria immitis, which is not possessed 

 of a sheath, wriggles precisely in the same manner. 



7. Some writers would lead you to imagine that there is but a 

 single pair of adult filarial in each filariated subject ; judging from 

 analogy of what occurs in other animals harbouring filarise, I 

 believe that there are generally a good many present, a dozen or 



1 Tropical Diseases — Cassell and Coy. Ltd., 1898. 



