100 ZOOLOGY 
The terminal proglottis breaks off from the rest of the 
Tapeworm owing to the contraction of its muscles, its rupture 
affects the transverse excretory duct of the segment in front, 
which is put into communication with the outer world, and thus 
forms the new terminal vesicle, which opens to the exterior. 
The ripe proglottis passes out of the alimentary canal of 
its host, and the eggs with which it is crowded escape by the 
rupture of its walls. In some species the free proglottides, 
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Fic. 68.—Development of Zaenia. From Leuckart. 
A, Cysticercus bovis, from beef. Natural D. Stages in the development of the 
size. brood capsules in Hehinococcus, 
B. Invaginated head of Cysticercus before «a. The thickening in the parenchyma of 
the formation of the suckers. the bladder. 
x 20. 6. Subsequent formation of a cavity in it. 
C. Invaginated head of Cysticercus cellu- c. Development of the suckers. 
losae, showing the bent head. x30. ad. A capsule with one head invaginated. 
e. A capsule with two heads. x 90. 
after they have left their host, retain a considerable power of 
movement, and crawl over blades of grass, ete. In this way 
their ova are disseminated, and stand a better chance of 
being eaten by their second host, in whose body alone they 
can develop. Some of them succeed in making their way, 
either by means of the food or water, into the stomach or 
