Economic Importance of Animals 539 



causing jaundice; the lungs, causing "thumps." This species is sometimes 

 called the human roundworm. 



Trichinosis is a human disease (also affecting pigs and rats) which 

 is produced by a certain order of roundworms (Trichinelloidea) when 

 they are eaten in inadequately cooked meat from infested pigs. These 

 worms are commonly called the "porkworm" (Fig. 100). 



Elephantiasis is a human disease in which the limbs and other regions 

 of the body swell to enormous size. This condition is caused by certain 

 roundworms known as Filaria worms (order Filarioidea) (Fig. 101). 



The hookworm disease is produced by a roundworm, Necator ameri- 

 canus (Fig. 99). Shiftlessness, loss of blood, anemia, a depraved appetite 

 for dirt, paper, and plaster are common symptoms. Probably 2,000,000 

 human beings are afflicted, especially in warmer climates. The hook- 

 worm larvae enter through the skin of the body, especially the feet. 

 Placing shoes on the feet of all persons will prevent the spread of this 

 very important disease. 



The human pinworm (Enterohius vermicularis) is a small, white 

 roundworm, the female of which is 10 mm. long and the male about 

 3 mm. long. It is still a debated question as to the relationship between 

 the larvae and eggs of the pinworm and appendicitis. 



Gapes is a disease of poultry and game birds which is caused by the 

 parasitic roundworm or "gapeworm" (Syngamus trachea). The round- 

 worm, Dictophyme renale, infests the kidneys of dogs, cattle, horses, and 

 man. The females of the species may be over three feet long. 



Heterodera (Caconema) radicicola attacks the roots of such plants 

 as potato, tomato, lettuce, turnips, and weeds, the irritation producing 

 the characteristic swelling known as root knot or root gall. 



The "vinegar eel" (Turhatrix [Anguillula] aceti) (Fig. 98) lives in 

 vinegar and other sour materials. It is frequently used in experimenta- 

 tion. 



PHYLUM 7— ROTIFERA OR TROCHELMINTHES 

 (ROTIFERS) (Fig. 102) 



Rotifers serve as food for higher forms of life. Certain Rotifers para- 

 sitize the intestine and coelom of worms as well as certain Crustacea 

 (phylum, Arthropoda) . Rotifers are frequently used in experiments on 

 bisexual and parthenogenetic development. Rotifers, in certain stages 



