206 FILARIA BANCROFTI [CH. 



V-spot is brought out by very light staining with dihite 

 logwood. The dye brings out yet another spot, similar to 

 the preceding, though very much smaller ; this second spot 

 is situated a short distance from the end of the tail. The 

 former I have designated the V-spot ; the latter the " tail 

 spot." Staining with logwood also shows the body of the 

 little animal is principally composed of a column of closely 

 packed, exceedingly minute cells enclosed in the transversely 

 striated musculo-cutaneous cylinder ; at all events, many 

 nuclei are thereby rendered visible. Dr Low has recently 

 pointed out to me that the break seen in all stained specimens 

 in the central column of nuclei occurs at a point slightly 

 posterior to the anterior V-spot. This break can only be 

 recognized in stained specimens." 



According to Annett, Button and Elliott, if preparations 

 of the living filaria are examined directly after being made 

 from the patient, the embryos are seen to exhibit, for a 

 short period, a rapidly progressive movement across the field 

 of the microscope — at first so rapid that the parasites can 

 only be traced with difficulty. This movement quickly ceases, 

 as the sheath of the embryo soon becomes attached to the slide, 

 as described above. 



The embryos vary from 270 to 340 a^ in length, by 7 

 to II /ti in breadth. 



Life-cycle in the vertebrate host. We shall commence with 

 the adult female in the lymphatics of the infected patient. 

 The fertilization is internal and the fertilized female usually 

 contains large numbers of embryos at various stages of 

 development. As this animal is ovi- viviparous, the eggs are 

 not liberated from the body of the parent until the embryonic 

 filariae (= microfilariae) are well formed and capable of inde- 

 pendent motion. The egg is surrounded by a transparent 

 sheath, within which the embryos are enclosed the whole 

 time they remain in the vertebrate host. The young filariae, 

 each enclosed in its sheath, on being liberated make their way 

 into the blood-vessels of the host and may be found in the 

 peripheral circulation. Whilst remaining in the blood they 

 are incapable of further development, but are enclosed 



