Il8 TROPICAL MEDICINE AND HYGIENE 



(2) Periodicity. The periodical recurrence of some of 

 the embryos is a striking phenomenon. In the case of 

 F. bancrofti it is definitely nocturnal, though a reversal 

 of the habits of the host will lead to a reversal of the 

 habits of the parasite (fig. 52). The embryo is often called 

 Microfilaria nocturna. In F. loa the periodical recur- 

 rence is in the daytime, and hence the embryo is known 

 as Microfilaria diurna (fig. 53). 



In the Philippines and in Fiji the embryos have no 

 definite periodicity, and though in other respects they 

 closely resemble Mf. nocturna, are possibly a distinct 

 species, and the embryos are described as those of the 

 F. philippinensis (figs. 54 and 55.) 



Bahr suggests that the absence of periodicity may be 

 connected with the day-biting habits of the intermediate 

 host, S. pseudoscutellaris. 



In determining periodicity it is essential that measured 

 amounts of blood should be taken. 



These three filarial embryos are all enclosed in a loose 

 sheath, and in life are indistinguishable from each other. 

 The measurements of the freshly dead, but not dried, 

 embryos are identical. 



(3) The filarial embryos not enclosed in a loose sheath 

 show no periodicity. These are readily distinguished 

 from each other, as in F. perstans the thin end tapers to 

 a blunt termination, whilst in F. demarquayi (and F. 

 ozzardi) the termination is an extremely fine-pointed tail. 

 In the sheathed human filaria the tail end is pointed, but 

 is said to be less so in the embryos in the Philippines 

 than in the others. 



(4) All the embryos have a core composed of nuclei 

 which stain deeply with haemalum or other basic stains. 

 This nuclear core does not extend to either extremity of 

 the embryo. 



The termination of this core at the head blunt end- 

 differs in the sheathed filaria. In Mf. diurna, the nuclei 

 are more closely packed together, are larger, oval, and 

 stain poorly, and anteriorly the core terminates abruptly, 



