NEMATODA 



219 



M. nigrescens Duj. (Fig. 349). Body 12 cm. long, .5 mm. thick, 

 attenuated anteriorly and blunt behind; color white, with the black 

 ovary showing through ; the young worms migrate on warm 

 summer days from the body of their hosts, often in large 

 numbers, into the moist earth, causing a belief that they 

 have rained down. 



Family 4. FILARIIDAE.* Fig. .349 



Mermis 



Body very long and filiform; mouth often surrounded "su/s^wfr! 

 by papillae or by 2 lips; no oesophageal bulb; male with 1 Deut.). 



spicule or with 2 of unequal size and with a spiral twist 

 of the hinder end; usually viviparous: several genera. 

 FiLARiA 0. F. Miiller. Vulva towards the forward 

 end; male with 2 spicules, and much smaller than the 

 female: numerous species, which live in man and other 

 vertebrates as final hosts, and probably in insects or crusta- 

 ceans as intermediate hosts ; Leidy mentions over 30 species 

 in this country. 



F. immitisf Leidy (Fig. 350). Length of male 18 cm.; 

 thickness .9 mm., with a corkscrew hinder end; length of 

 female 30 cm. ; thickness 1.3 mm. : in the heart and veins of 

 the dog, the .28 mm. long larvae appearing in the blood, 

 especially in the night time ; the larvae are transferred from 

 one dog to another by mosquitoes; very common in China 

 and Japan, and occurring in America and Europe; it some- 

 times infects man. 

 F. bancrofti Cobbold (Fig. 351). Male 

 4 cm. long, .1 mm. thick and colorless; 

 female 8 cm. long, .28 mm. thick and 

 brownish in color: in the heart and lymph 

 vessels of man in the tropics, also in the 

 southern United States, the .3 mm. long 

 lan^ae appearing in the blood, but in the 

 surface circulation only at night ; the larvae 

 are transferred from one person to an- 

 other by mosquitoes; one of the causes of 

 elephantiasis. 



F. loa (Cob.). Male 30 mm. long, .4 mm. thick, with 8 large cir- 

 cumanal papillae; female 41 mm. long and .5 mm. thick; body with 



* See "The Zoological Characters of the Roundworm Genus Filaria," etc., by 

 C. W. Stiles, Bull. 34, Hygienic Lab., etc., 1907. 



t See "Notices of Nematoid Worms," by J. Leidy, Proc. A. N. S., Phila., 1886, 

 p. 308. 



Fig. 350 

 Filaria 

 immitis 

 (from Braun). 

 A, male 

 B, female. 



Fig. 351 — Filaria tancrofti 



(from Braun), showing 



several worms among 



blood corpuscles. 



