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various sizes, the smallest types are represented by the so- 

 called vinegar and paste eels, whilst others have been seen 

 several feet in length. About 550 species have been described 

 in the eight families. About the best known is called Tricho- 

 cephalus dispar, which belongs to the fourth family, the Filaridce. 

 The anatomy of this worm was minutely described, as also 

 that of the well-known Nematoid worm, the Trichina spiralis, 

 the cysts of which, when introduced into the stomach of an 

 animal, attain their sexual maturity in about forty-eight hours, 

 and the viviparous females become parents in about six days. 

 The young then penetrate through and take up their abode 

 in the voluntary muscles, where they become encysted, and 

 remain coiled up within them, waiting to become devoured by 

 some other animal. If not released, after a time they break up, 

 and become transformed into carbonate of lime. Leuchart 

 found in one ounce of muscle 325,000 individuals of this 

 species. 



The fourth order, the Acanthocephala, contains no types 

 infesting man, although they have been found in mammals; 

 birds and fishes are most troubled with them. They are small 

 animals, having elongated bodies, marked by transverse folds. 

 At the head is a long mouth or proboscis, armed with recurved 

 hooks, and in the male there is a peculiar clasping organ to 

 assist it in the sexual act. The embryo is a pear-shaped organ- 

 ism, and develops within its own interior a small Echino- 

 rhyncns : the original body becomes part of the new develop- 

 ment, and only the old skin is cast off. When transferred to 

 the body of another host it becomes sexually mature in about 

 a week. 



The Cestoda, the fifth order, comprises the so-called tape- 

 worms, which are distinguished by their soft, flat, long bodies, 

 divided into joints, the anterior of which forms the head and 

 neck. The head, which is exceedingly small when compared 

 with the length of the animal, is furnished with four suckers, 

 and sometimes a double crown of hooks. The joints at the 

 posterior end are capable of existing independently and of 

 developing ova. Cestoda are found either in the larval or 



