FILARIAL EMBRYOS 121 



whilst in Mf. nocturna and the embryos of F. philippi- 

 nensis (?) there are detached nuclei at the anterior 

 termination and the nuclei are smaller, more rounded 

 and stain more clearly. (Plate I.) 



(5) Measurement of the living or freshly dead embryo 

 differs a good deal from those that have been allowed to 

 dry on a slide. Mf. diurna shrinks more than the other 

 sheathed microfilariae, and therefore in stained specimens 

 is actually smaller, and in proportion to the sheath which 

 does not shrink considerably smaller than the others. 



(6) The position assumed by the embryo when dying is 

 capable of being modified by exposure to various vapours, 

 or, as Fulleborn has shown, merely by the rate at which 

 the film is dried. In blood films prepared in the usual 

 w T ay and air-dried there are striking differences. Mf. noc- 

 turna and F. philippinensis (?) die in bold, graceful curves, 

 whilst in Mf. diurna the attitude assumed is less graceful, 

 as they are only slightly bent, and often show irregular, 

 angular bends, particularly at the tail end. 



Examination of a single embryo may lead to an "in- 

 correct conclusion occasionally, but in the majority of 

 instances it is easy to distinguish Mf. diurna from the other 

 two. Between Mf. nocturna and F. philippinensis (?), except 

 for the periodicity, no constant appreciable differences 

 can be observed. 



Between the sharp-pointed, sheathless embryos of F. 

 demarquayi and F. ozzardi po differences can be observed. 

 It is doubtful if they are distinct species. 



It is noteworthy that F. loa and F. bancrofti have few 

 points of resemblance, though their embryos are indis- 

 tinguishable from their appearance and measurements 

 whilst alive, and when dead and stained are recognized 

 only by minor differences. Fulleborn has shown that 

 there are further differences in the nuclei and cells, both 

 excretory and genital, contained in the nuclear core 

 which are developed when " vital " stains are used. 



Exclusion. It is often important in obscure cases to be 

 able to exclude the possibility of even a small infection 



