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 trichinas, 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 



m < ' 



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 



,.,. ,, , , ,, , TT .. .,,. 



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 

 spiral-is (male enlarged). 



