CHAPTER V 



DISEASES DUE TO NEMATODES (EELWORMS) 



Nematodes are worms of relatively simple structure, typically 

 slender and cylindrical in shape, as indicated in the popular 

 names eelworm and threadworm, although in certain stages 

 some species may become swollen into gourd-like or other forms. 

 Nematodes are hatched from eggs, usually outside the body 

 of the female, have a larval stage in which the sex organs are 

 not developed and a sexually mature stage in which there is 

 usually more or less difference in size or form between the male 

 and the female. It must be noted, in view of the unfortunate 

 American usage of the word worm for caterpillar, which has 

 gained considerable currency in the West Indies, that nematodes 

 are not stages in the development of insects or of anything else : 

 they are and remain worms. 



As is the case with the fungi, the order contains a large 

 number of species which live in soil or water or on decaying 

 vegetable or animal remains, and others which are parasitic to 

 various degrees. While the parasitic fungi mostly attack plants 

 and are comparatively rare on animals, the greater number of 

 nematode parasites are found in animals, and a much smaller 

 number are known as the cause of injury or disease in plants. 



In animals of all descriptions particular nematodes inhabit 

 the blood, the muscles, the stomach and intestines, the lungs, 

 the heart and other organs, and among them are such notorious 

 organisms as Ascaris, Strongylus, Trichina, Ankylostoma and 

 Filaria. 



Nematode diseases of plants have lacked adequate attention 

 owing to their position in a no-man's-land between the entomo- 

 logist and the mycologist, but recognition of their variety and 

 importance is growing. One species which has become well 

 known is Heterodera radictcola, which infests and damages the 

 roots of more than 500 known host plants. It is more usual, 

 however, for a given species to be restricted to a few hosts or 

 to one only. Where several are attacked a certain amount of 

 biologic speciahsation has in some cases been observed, some 

 difficulty being apparent in the accommodation of a strain bred 

 on one plant to a host of another species. 



In recent years the investigations of N. A. Cobb have brought 

 to light the fact that predaceous nematodes exist, some of which 

 feed on other nematode species injurious to agriculture. This 

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