FILARIA BANCRdFTI 



635 



They measure from 290 to 320 fji in length and from 7-5 to 8-4 {a, in 

 breadth (Low), and are seen to be long, slender, cylindrical organisms 

 with a rounded anterior and a tapering posterior end, enclosed in 

 a sheath— the vitelline or egg membrane— inside which they are 

 capable of darting backwards and forwards, because it is longer 

 than they are, the empty portion being noted either in front of 

 the anterior or behind the posterior end of the Microfilaria . Manson 

 considers that this sheath is of vital importance to the little parasite, 

 as it prevents its using its anterior spine to escape out of the blood- 

 vessel, and so losing the chance of its invading a mosquito. 



The anterior rounded extremity is said to possess a thick hemi- 

 spherical proboscis, carrying a minute apical spine, which is capable 

 of being covered by a retractile and protractile six-lipped prepuce, 

 but this observation requires confirma* ion. 



Behind the anterior end, the body can be seen to be composed 

 of a transversely striated dermo-muscular layer, inside which are a 

 number of closely packed cells whose nuclei show up clearly on 



Fig. 268. — Diagram of the Development of a Microfilaria 

 [Loa loa Stiles). 



(After Penel.) 



staining. Unstained, the central mass appears granular, but the 

 granules are, however, wanting at certain spots, which, following 

 Annett, Dutton, and Elliot, may be defined as: (i) A clear anterior 

 ar-ea from the front to the first nuclei; (2) an irregular transverse 

 spot situated 21-5 per cent, of the length of the body from the 

 anterior end; (3) a V-shaped or transverse irregular spot at 30 per 

 cent, of the length, called V-spot by Manson; (4) a median line, the 

 central viscus of Manson, whose centre is at 63 per cent, of the 

 length; (5) an irregular oval spot often present at 85 per cent., 

 called the tail-spot by Manson; (6) a small central spot only occa- 

 sionally present at 91-7 per cent.; (7) the clear posterior area 

 behind the last nucleus. 



Leiper points out that these areas are not peculiar to the Filaria 

 embryos, but occur also in other forms. The V-spot is the excretory 

 vesicle and the tail-spot the proctodseum. The morphology of the 

 worm has been studied in detail by Fiilleborn, whose diagram 

 s reproduced on p. 637. 



