454 
WORMS. 
Dochmius duodenalis. a, Entire ; b, Head (enlarged); 
c, Tail (enlarged). 
reach in this host a length of about one-twelfth of an inch, their complete 
development only taking place after the swallowing of the infested Cyclops by a 
fish. Another member of the same family is the Syngamus 
trachealis, which owes its double name to the fact that the 
males and females are found in pairs in the windpipes of 
various birds. They sometimes occur in such numbers that 
the inflammation set up by their blood-sucking suffocates their 
host. The eggs appear to be brought up into the bird’s mouth 
by crowing, or by the choking cough that the presence of their 
parent causes. 
They are then 
swallowed, and 
pass out through 
the alimentary 
canal. As soon as 
they have obtained 
sufficient damp¬ 
ness and warmth, 
they develop in 
about a week’s 
time into small 
thread-shaped em¬ 
bryos, with a blunt head and pointed tail. These obtain an 
entrance into another, or the same bird’s mouth with the food, 
and thence pass into the windpipe. 
Perhaps the most dangerous of all human internal parasite 
worms is Trichina spiralis. In the mature stage these 
creatures live in the intestines of mam¬ 
mals and birds, where they propagate and 
gradually perish. The females are about 
one-eighth of an inch long, and twice 
the size of the males. In both sexes 
the mouth lies at the front end of the 
body, which is its narrowest part; the 
tail is stumpy, and in the male provided 
with a pair of short processes. The 
number of progeny produced by one 
female may amount to some thousands, 
and as soon as these are born they make their way into the 
blood-vessels of their host’s intestine, where they are carried 
by the circulation to some more distant part of the body, and 
ultimately come to a stop in one of the muscles. Here by 
feeding they grow in a few weeks to four times their original 
size, and form between the muscular fibres a great cyst 
or capsule, in the centre of which the worm lies coiled up in a spiral. It has 
not been ascertained how long the creature can remain in this immature state, but 
HEAD OF Cucullanus 
elegans (enlarged). 
HUMAN THREAD - WORM, 
Oxyuris veriniculciris 
(much enlarged). 
