620 ARTICULATA. 
Class VII- NEMATEI.MIA. 
The term Nematehnia signifies Bound- Worms, and includes species of a more or less elon- 
gated, cylindrical form, with a thick, strong, and wrinkled skin, which gives the body an annu- 
lated appearance. As far as our present knowledge goes they are unisexual. They not only 
inhabit the intestines of other animals, but many species are also to be met with in the interior 
of completely closed organs, to which they must have obtained access in their earliest stages. 
They form three distinct orders, the JVematoidea, the Gordiacea, and the Acanthocephala. 
ORDER 1. MEMATOIDEA. 
This term means " resembling a filament,^'' and the order consists principally of worms parasitic 
in the intestines of other animals. It includes the common Round- Worm or Ascaris of the hu- 
man subject, as well as the little Thread- Worm — Oxyuris — which is often so troublesome to 
children. The Strongylus gigas sometimes attains a length of two or three feet and the thick- 
ness of a man's little finger, and usually inhabits the kidneys of swine, but sometimes finds its 
way into the same organ in man. It is often fatal to its host. 
This order also includes the dreaded Guinea-Worm, Filaria medinensis, which appears to 
occur in most parts of tropical Africa. It lives in the cellular tissue beneath the skin, and be- 
tween the muscles of man, confining its attacks principally, though not exclusively, to the lower 
extremities, where it often produces considerable pain. It is said occasionally to attain a length 
of twenty or thirty feet, but its average length is five or six. 
In this order we also place the Angiiillulidce, the so-called Eels of paste and vinegar. These 
are minute, thread-like worms, exhibiting distinct digestive and generative organs, and which 
occur often in great numbers in putrefying substances. 
ORDER 2. GORDIACEA. 
The Gordiacea, or Hair- Worms, are at once distinguishable by the extraordinary length of 
their bodies, which frequently present a close resemblance to a horse-hair; so close, indeed, 
that in former times the popular belief ascribed their origin to the introduction of horse-hairs 
into the water in which they were found. They live as parasites in the bodies of various species 
of insects. They sometimes become completely dried up, and appear dead, but come to life 
again and start off with great activity when refreshed by a shower of rain. 
ORDER 3. ACANTHOCEPHALA. 
This order, which includes only a single genus, is composed of parasitic worms often of con- 
siderable size, which find their habitation in the intestines of various animals, especially fishes. 
One species, the largest in the order, is common in the intestines of swine, where it sometimes 
attains a length of eighteen inches. 
Class VIII. X*I.AT¥EI.MIA. 
The Platyelmia, or Flat- Worms — a branch of the Entozoa'^ — include three orders, the Plan- 
arida, the Trematoda, and the Cestoidea. 
* The term Mitozoa is from the Greek term entos, within, and zoon, an animal ; as used by naturalists it includes 
generally, the internal parasites. 
