NEMATHELMINTHES 235 



diseases produced by these animals are extremely seri- 

 ous. Trichinosis is due to infestation by the small 

 nematode Trichinetta, which we get through eating in- 

 fested pork which has not been sufficiently cooked. 

 The notorious hookworm of the Southern states is also 

 a nematode. 1 So also is the African Guinea worm, 

 which lives first in a minute fresh-water crustacean 

 (Cyclops), and is swallowed by man in drinking water. 

 Another species infests man and the mosquito alter- 

 nately. A nematode, attacking the roots of plants, 

 produces swellings or galls. Another is very injurious 

 to the sugar beet. 



The structure of nematodes is quite complicated, so 

 that Dr. Cobb, in making a diagram of the anatomy, is 

 able to enumerate no less than 116 distinct parts. For- 

 tunately the small species are transparent, so that the 

 various organs can be seen in the living animal. 



References 



COBB, M. A. "Nematodes and Their Relationships." Yearbook United 

 States Department of Agriculture for 1914. For a well-illustrated ac- 

 count of the genera, see WARD and WHIPPLE, Fresh-water Biology. 1918. 



ROTATORIA 



I. The Rotatoria, or rotifers, are minute aquatic structure of 

 animals which may be taken for Protozoa, unless atten- arotifer 

 tion is paid to their anatomy. They seem to have 

 "wheels in their heads," owing to the presence of con- 

 stantly moving cilia arranged in a circle around the 

 anterior end. As they are usually quite transparent, 

 it is easy to see the chitinous gizzard or mastax, the ali- 

 mentary canal, reproductive organs, etc. The common 

 free-swimming forms have a short bifurcated or two- 



1 See the publications of the Rockefeller Sanitary Commission for the 

 Eradication of Hookworm Disease. 



