44 BRANCH NEMATHELMINTHES 



Oordius, the " hair-worm," is found in watering-troughs and erroneously 

 believed by superstitious people or those ignorant of biologic principles to 

 be horse hairs transformed into live worms. The larvae are parasitic in 

 the grasshopper, the adults live in water. Agassiz tells of experimenting 

 with one IS inches long which was wrapped in and out of its eggs, which 

 were rolled up into a ball about the size of a coffee bean. He disentangled 

 it and it " sewed " itself through and through the little white mass. Three 

 times he separated the worm from its eggs, and each time the process of 

 entangling was repeated, convincing Agassiz that there was a definite 

 purpose in its attempts, and that even a being so low in the scale of animal 

 existence has some dim consciousness of a relation to its offspring.' 



He placed a small portion of the egg mass under the microscope, and 

 estimated that there were not less than 8,000,000 eggs in the whole mass, 

 which, when unwound, made a string 12 feet long. 



CLASS n. ACANTHOCEPHALA 



Most of the class Acan'thoceph'ala are small parasites. The 

 chief genus (Echinorhyn'chus) is parasitic in the intestines of 

 mammals, birds, reptiles, amphibians, and fishes. The largest 

 species is found in the pig, and one species, EcMnorhyncfms 

 hominis, is extremely rare in man. 



CLASS m. CH.£TOGNATHA 



This class contains but two genera of curious arrow-shaped 

 worms, all but one species of which are pelagic. They are 

 hermaphroditic and have three pairs of ccelomic pouches, 

 " fins," and bristle-like jaws. 



Economic Importance. — In this branch may be found worms 

 which are harmful and those which are helpful to man. Those 

 forms like Trichinella spiralis, which are parasitic in man, are 

 very injurious. The only preventive upon which it is safe to 

 rely is thorough cooking. 



Those forms which infest wheat and turnips are also harmful 

 to man, in that they destroy his food; while Gordius, which is 

 parasitic in the grasshopper, is indirectly beneficial to man. 



Important Biologic Facts. — For the first time in the scale of 

 animal life, a caelom, or body cavity, appears. It is filled with a 

 clear fluid, and through it extends the straight alimentary tube 

 which consists of pharynx or stomodeum, an intestine, and a 

 rectum. There are no circulatory and no i-espiratory organs. 



1 "Methods of Study in Natural History," Agassiz, pp. 63, 64. 



