PARASITES OF ANIMALS. 



95 



the intestinefof one dog, so that they make up by numbers 

 what they lack in size. Such a dog is constantly discharging 

 and scattering thousands or millions of the extremely mi- 

 nute eggs of this tape-worm wherever he goeskJ^Tf^JBJR 



/%**' -^ 



Fiirare 68. 



JLibrary 



They are scattered among the grass in fields and pas- 

 tures ; they get into the water of brooks and springs ; they 

 are liable to adhere to fruit that has fallen, or to lettuce 

 and other garden vegetables. 



Dr. Cobbold has calculated the number of progeny that 

 might proceed from one egg during a single generative cycle. 

 Allowing 500 secondary cysts to be formed and 10,000 

 heads or scolices to be developed by each hydatid cyst of 

 average size, these might produce 5,000,000 tape-worms, 

 each of which having three joints that become free, would 

 give 15,000,000 joints or proglottides, and if each of these 

 contains 10,000 eggs, the whole number of eggs in one gen- 

 eration, would be 150,000,000,000! 



Figure 68. Echinococcus heads attached to inside of brood-capsule, greatly 

 magnified. Hearth and Home, after Thudichum. 

 Figure 69. A head or scolex, becoming a brood-capsule. From Leuckart. 



