166 



BIOLOGY FOR BEGINNERS 



PARASITIC WORMS 



In this group are included the tapeworm, trichina, hookworm, 

 and many others. As is often the case, they are harmful because 

 parasitic. A parasite, as has been said, 

 takes the nourishment of another creature 

 instead of getting its own. 



Tapeworm. The tapeworm lives first 

 within the body of pigs or cattle, the egg 

 being taken in with their food. It develops 

 in the intestine, bores its way into the 

 muscles and goes into a resting stage. 

 If the flesh of such animals be eaten when 

 not thoroughly cooked the development 

 continues in the intestine of man, where 

 the worm attaches itself by hooks on its 

 head, lives on the digested food with which 

 it is surrounded and by robbing its host of 

 needed nourishment, produces segment after segment till a length of 

 thirty to fifty feet may be attained. These segments are practically 



FIG. 52. Encapsuled 

 trichinae in trunk muscle 

 of pig. (Greatly magni- 

 fied, after Braun.) From 

 Kellogg and Doane. 



FIG. 53. Hookworm, Necator americanus. a, Male; b, female. (Greatly 

 enlarged; after Wilder.) From Kellogg and Doane. 



sacs of eggs which break off from time to time, allowing the eggs 

 to escape, dry, and scatter, where hogs or other animals may eat 

 them and start the circle over. 



