^Y20 AliTTCULATA. 



CUtss YII. ]lfEI?IATi:i.]fIIA. 



Tho term Xcmatclmia signifies i?0Mwc?- PTon??*, aiul iiiclucles species of a more or less elon- 

 fjutetl, rvliiitlricnl form, with a thick, strong, and wrinkled skin, which gives the body an annu- 

 iatcd 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 tlieir earliest stages. 

 Tlicv l"orm three distinct orders, the JVcmatoidca, the Gordiacca, and the Acanthocephala. 



ORDER ]. NEMATOIDEA. 



Tliis term motiTM^ " rcscmbli)/;/ a filament,'''' ami 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 — Oxi/uris — which is often so troublesome to 

 children. The Stron{iylus g'lgas 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 

 wav into the same organ in man. It is often fatal to its host. 



This order also ineludes 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 AnguilluUdce, 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. Tliey 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 Till. X*I.ATYEI.IfIIA. 



The Platyehnia, or Flat- Worms — a branch of the Entozoa* — include three orders, the Plan- 

 arida, the Trematoda, and the Cestoidea. 



* The term Entozoa is from the Greek term entos, within, and zoon, an animal ; as used by naturalists it includes 

 generally, the internal parasites. | 



