264 



CIVIC BIOLOGY 



Tapeworms of the dog Tctnia echinococcus. Unfortunately our faith- 

 ful friend has been found to harbor twelve different species of tapeworms. 

 The most dangerous of all is T. echinococcus, which has a different life 

 history and mode of growth from those just described (see Figs. 116, 117). 

 The adult worm is minute (from 2.5 to 6 millimeters long) and occurs 

 only in the dog, wolf, and jackal, often in enormous numbers. The 

 cysticercus stage is found in twenty-seven different mammals, including 

 man. Instead of forming a cyst with a single sco- 

 lex, or head, this worm forms a cyst that may 

 grow for several years, to the size of a goose egg 

 or even a " child's head," and its wall forms num- 

 bers of vesicles which may develop hundreds of 

 scolices. Dogs infested with this tapeworm should 

 be mercifully killed and cremated, and dogs, 

 generally, should not be permitted to lick the 

 face or hands or to eat out of dishes used by man. 

 Tapeworms of fishes Dibothriocephalus latus. 

 Fishes harbor a number of tapeworms, which, 

 chiefly in oriental countries, naturally find their 

 way into men, who consider raw fish a delicacy. 

 The broad tapeworm, D. latus, is found in the 

 muscles of various fresh-water fishes, among 

 them the pike, salmon, and perch. 



Tapeworms vary in size from almost micro- 

 scopic to ribbons half an inch broad and many 

 feet in length, but this signifies little. The rate 

 of growth for T. saginata and D. latus has been 

 determined as 7 centimeters and 8 centimeters 

 per day respectively. At this rate, in thirty-five 

 years a broad tapeworm might grow to be 

 3406.6 feet in length. 



FIG. 116. Dog tape- 

 worm ( T. echinococ- 

 c us), twenty-five times 

 natural size 



After Braun 



Roundworms (nematodes) and threadworms (nemathelminthes) 

 (nema, " thread "; helminthes, " worms"). These worms attack 

 plants, all sorts of animals, and man, and are the real terrors 

 among vermian parasites. One species, Heterodera radicicola, 

 has been found infesting the roots of four hundred and fifty 

 different plants, the list including all garden-truck crops, 

 many field crops, and a great variety of fruit trees, orna- 

 mental trees, shrubs, and flowers. They infest greenhouses 



