2OO ZOOLOGY 



reproduction takes place again, the embryos migrate into the muscles and the new 

 cycle is begun. We do not find here the non-sexual reproduction that helped make 

 the Liver-fluke so prolific, but the reproductive power of Trichinella is very great 

 without this. It is estimated that an ounce of "measly " pork may contain 80,000 

 cysts of Trichinella, and that each female produced from these embryos may con- 

 tain at one time 1,000 or more embryos. During her life she may produce ten 

 times this number. Thus the 40,000 females from such a meal would soon supply 

 40,000,000 young worms for the infection of the muscles, with the ability of renew- 

 ing the supply at short periods. Perfect cooking is the only sure safeguard against 

 the possibility of infection. 



The hookworm, Necator americanus, belongs to this phylum and is a common 

 parasite of man in the southeastern states. It has only one host in its life cycle. 

 The adult worms attach to the wall of the intestine with a sucker-like mouth. 

 The teeth pierce the wall and the esophagus works as a pump to extract the blood. 

 From the mouth, secretions are poured that prevent the blood from clotting. 

 In this way the wound may continue to bleed after the worm goes to a new spot. 

 One worm may thus make many wounds ; and in some cases more than a thousand 

 have been found in one person. The female may produce thousands of eggs, but 

 these cannot develop in the intestine of man. They pass from the intestine, and 

 then hatch and undergo their early development in the moist soil. If they do not, 

 at a certain stage, find their way back into man or some similar host they die. 

 Possibly they may get back into the intestine on raw vegetables, but a much more 

 wonderful way has been demonstrated. It has been found that they can pene- 

 trate the skin, and many of the poorer people go barefoot in these regions. The 

 larvae bore into the capillaries, are taken to the heart and go with the blood to the 

 lungs. Here they bore into the lung cavity, pass up the bronchial tubes, through the 

 trachea into the gullet and on into the intestine. It takes about seventy days from 

 the time the larvae enter the skin until a new generation of eggs appear from the 

 intestine. The effect of infection upon human beings is bloodlessness, weakness, 

 deranged digestion and poor nutrition, abnormal appetite, and laziness. 



It has been found that the worms may be driven from the intestine by thymol, 

 which stuns the worms and makes them loosen their hold, followed by epsom salts 

 which flushes them from the intestine. Thymol, however, should be taken only 

 by the prescription of a physician as it acts strongly on the heart. Prevention of 

 infection involves stopping the miscellaneous infection of the soil by discharges 

 from the intestine and protecting the skin from exposure. Drouth and freezing 

 are fatal to the larvae. 



Phylum VI: Trochelminthes (wheel-worms or rotifers'). The Rotifers or wheel- 

 animalcules are microscopic animals. They usually tend toward bilateral sym- 

 metry. The anterior end possesses a retractile disc supplied with cilia variously 

 arranged, the rhythmic motions of which often give the appearance of a rotating 

 wheel. From this the name of the group comes. This organ assists in locomotion 

 and produces currents in the water by which food is brought within reach of the 

 mouth. There is a digestive tract with both mouth and anus. The pharynx into 

 which the mouth opens is provided with a chitinous grinding apparatus (mastax). 

 Usually a pair of digestive glands open into the stomach. The nervous system is 

 usually limited to a single ganglion dorsal to the pharynx. Eye-spots and other 

 sense organs, called tactile rods or antennae, are present. There is a true ccelom 

 communicating with the exterior by means of excretory tubules. For a diagram- 

 matic view of these structures see Fig. 95. 



