THREAD- WORMS. 



455 



TRICHINOSIS WORM COILED UP IN HUMAN 



muscle (enlarged). 



certainly for years, and perhaps decades. It can, however, develop no further 



until introduced into the intestine of a suitable host. For instance, if the muscles 



of a pig be infested with trichinae, and eaten in an uncooked state by a human 



being, the immature worms are set free in the intestine of the new host, where 



they grow to matu- 

 rity, and produce 

 young. To the 

 genus 'Filaria be- 

 long two other 

 worms parasitic 

 upon man, and the 

 cause of sickness. 

 One commonly 

 known as the 

 guinea -worm, and 

 occurring in the 



tropical and subtropical countries of the Old World, lodges 



itself beneath the skin, producing abscesses. It may attain 



a length of several feet, and the operation of extracting it 



from the patient demands considerable skill and patience. 



The second species lives in the blood and lymphatic vessels, 



and is said to cause elephantiasis. The larvae are sucked from 



human blood by mosquitoes. When the insects perish, the 



worms make their escape into water, where they attain 



maturity and produce their young, which are subsequently 



taken into the human body when the water is drunk. 



The family of hair-worms, Gordiidce, owe their English 



name to the resemblance that their long, black, slender, flexible 



body bears to a hair from a horse's mane or tail, and their 



scientific title, Gordius, to the peculiar habit the animals 



have of tangling and entwining themselves in a way that 



may be compared to a Gordian knot. The best -known 



species is G. aquaticus, the average length of which is about 



4 inches, although specimens three times that length have 



been obtained. The width of a male is about one-thirtieth 



of an inch, the females being slightly wider. The prevailing 



colour is brown of various shades ; the males, however, are 



always darker and more polished than the females, and are 



often of a deep shining black, while the females vary from 



light yellow to deep yellow-brown. Upon the middle of 



the abdomen, both in males and females, runs a long dark 



streak, visible even in the darkest males. Another mark by which the male 



may be recognised is the bifurcated tail end. Although living a free life in 



the adult condition, these worms spend the greater part of their lives, up to the 



last period, in certain insects. The young hair-worms, as they issue from the 



egg, are scarcely more than one twenty-fifth of an inch in length, and most 



trichinosis worm, Trichina 

 spiralis (male enlarged). 



