290 



THE ANIMAL PARASITES OF MAN 



the time of flying of certain insects. The flowers of Hesperis tristis, 

 and other flowers which are visited by small nocturnal moths, give 

 off no scent during the day, but exhale a strong hyacinth odour at 

 twilight ; on the other hand, many flowers visited during the day 

 become scentless' at night. L. W. S.] 



It is an interesting fact that the appearance of the filariae in 

 the peripheral circulation tallies with the swarming period of the 

 mosquitoes, and this affords the mosquitoes the opportunity ot 

 extracting some of the filariae from the body of human beings 

 whilst sucking their blood ; others, again, through the blood vessels 



of the glomeruli, attain the 

 urinary tubules and escape with 

 the urine. This, however, only 

 appears to be an unusual way. 



The filariae appear in the blood 

 in great numbers 140,000 ac- 

 cording to Lewis's calculations, as 

 many as 30,000,000 40,000,000 

 according to Carter and Mac- 

 kenzie, provided, however, al- 

 ways that their number in the 

 total quantity of blood is evenly 

 distributed and equal to the 

 average contained in the blood 

 tests. 



By observing in the moist cham- 



FIG. 197. Larvae of the Filana ban- 

 crofti in the blood of Man. Magnified, ber a drop of blood containing 



(After Raiiiiet.) filarial larva, it will be seen that 



after a little time, namely, when 



the haemoglobin from the blood corpuscles appears in the plasma, 

 the filariae escape from their sheaths ; a six-lipped collar is then 

 distinguishable at their anterior extremity, surrounding a conical and 

 fairly thick rostellum, at the point of which there is a retractile 

 filament. This complicated structure appears to be especially adapted 

 for boring through and dilating the tissues. It comes into action 

 when the filariae have reached the intestine of mosquitoes, 1 where 

 the above-mentioned alterations of the blood take place. The 

 filariae, which have escaped from their sheaths, bore through the 

 intestinal wall and settle amongst the thoracic muscles of the 



1 The species in question are stated to be Culex ciliaris, L. ; Culex skusi, Giles ; Culex 

 taniatus, Meig. ; and Culex fatigans, Wied. 



[C. ciliaris. L. = C. pipiens, L. ; C. skusi, Giles = C. fatigans, Wied. ; C. taeniatus, 

 Meig, = Stegomyia fasciata, Fabr. F.V.T.]. 



