PARASITES OF ANIMALS. 95 
the intestine"of one dog, so that they make up by numbers 
what they lackin size. Such a dog is constantly discharging 
and scattering thousands or millions of the extremely mi- 
nute eggs of this tape-worm wherever he goes. et 
Figure 68. - 
Figure 69. 
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. 
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