UNSEGMENTED WORMS 20I 



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

 cycle is begun. The reproductive power of Trichinella is very great. It is esti- 

 mated that an ounce of "measly" pork may contain 80,000 cysts of Trichinella, 

 and that each female produced from these embryos may contain 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 renewing 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 mian 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. 

 This adds greatly to the loss of blood. 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 remarkable way has been demon- 

 strated. It has been found that they can penetrate the skin, and many of the 

 poorer people go barefoot in these regions. The larvs bore into the capillaries, 

 are taken with the blood to the heart and thence 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. 



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 larvte. Recent investigations have shown 

 that at least under some circumstances, certain domestic animals (pigs, chickens) 

 play a part in disseminating the eggs and larvas. 



Phylum Trochelminthes {wheel-worms or rotifers). — The Rotifers or wheel- 

 animalculps 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. Prom 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 coelom 

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

 matic view of these structures see Fig. 95. 



The sexes are distinct and are frequently very different in appearance. The 

 males are often much smaller than the females, are much less numerous, and are 



