CHAPTER 23 



THE PHYLUM NEMATHELMINTHES 

 AND RELATED PHYLA 



The worms of this phylum, commonly known as the nematodes, 

 can be easily separated from those of the other worm phyla by their 

 slender, pointed, threadlike bodies. With but few exceptions, they 

 are very tiny with both free-living and parasitic species usually under 

 a millimeter in length ; however, a few parasitic species do attain 

 lengths as great as a meter. 



The nematodes are among the most abundant of all animals. They 

 live everywhere ; in fact, it has been estimated that an acre of good 

 soil may contain 3,000,000,000 nematodes. They are found not only 

 in the soil, but in both fresh and salt waters, in the roots, stems, and 

 leaves of plants, and as parasites in the organs of nearly all species of 

 animals. Dr. Cobb, an authority on this group, has dramatically 

 summarized their abundance as follows : 



"In short, if all the matter in the universe except the nematodes 

 were swept away, our world would still be dimly recognizable, and 

 if, as disembodied spirits, we could then investigate it, we should find 

 its mountains, hills, vales, rivers, lakes, and oceans represented by a 

 film of nematodes. The location of towns would be decipherable 

 since for every massing of human beings there would be a correspond- 

 ing massing of certain nematodes. Trees would still stand in ghostly 

 rows representing our streets and highways. The location of the vari- 

 ous plants and animals would still be decipherable, and, had we suffi- 

 cient knowledge, in many cases, even their species could be de- 

 termined by an examination of their erstwhile nematode parasites. 



"We must therefore conceive of nematodes and their eggs as 

 almost omnipresent, as being carried by the wind and by flying birds and 

 running animals ; as floating from place to place in nearly all the waters 



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