THREAD- WORMS. 
455 
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 
To the 
Filaria be- 
two other 
worms parasitic 
upon man, and the 
cause of sickness. 
One commonly 
known as the 
guinea-worm, and 
the 
young. 
genus 
long 
TRICHINOSIS WORM COILED UP IN HUMAN 
muscle (enlarged). 
occurring 
m 
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. aquations, 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). 
