182 PRACTICAL ZOOLOGY 



sheep (Fig. 103, A) causes the production of numerous small 

 nodules in the walls of the large intestines. These are some- 

 times mistaken by government inspectors in slaughterhouses 

 as evidences of tuberculosis. Dogs are frequently attacked by 

 worms of the genus A scar is to which the parasitic roundworm 

 of man also belongs. Breeders of fancy dogs lose many valuable 

 animals because of the attacks of these worms. Other round- 



Fig. 103. — Parasitic roundworms. 



A, nodular worm of sheep ; B, stomach worm of sheep ; C, worms that cause 

 gapes in poultry ; D, hookworm. 



worms live in the soil and cause growths called galls to form on 

 the roots of plants. 



Characteristics and Classification. — The roundworms or 

 threadworms belong to the phylum Nemathelminthes. They are 

 usually long and slender and more or less cylindrical. They are 

 unsegmented, both externally and internally, and hence easily 

 distinguished from the annelids or segmented worms. Many 

 roundworms are parasitic in habit, but others live in water or 

 decaying vegetable and animal substances. 



REFERENCES 



Cambridge Natural History, Vol. IT. — The Macmillan Co., N. Y. City. 

 Bulletins of Bureau of Animal Industry, U. S. Department of Agriculture. 



