52 



VARIOUS FORMS OP TAPEWORMS. 



the cysts into the stomach of the dog. The cyst Echinococeus 

 veterinorum (Sieh.) is the same as E. polymorphus of Diesing. 

 They are to be met with in man, monkeys, cats, dogs, rabbits, 

 sheep, oxen, goats, horses, deer, and many 

 foreign animals; but ruminants and pigs are 

 the greatest sufferers Man in certain dis- 

 tricts, especially in Iceland and Ln Mecklen- 

 burg, has often suffered seriously from this 

 so-called Hydatid plague. Although Echino- 

 coceus is met with in all parts of the body, it 

 is the liver that is chiefly invaded : occasion- 

 ally much pathologic disturbance is also caused 

 by them in the lungs and in the kidneys. . 



The ova of Tcenia echinococeus are passed 

 out with the ripe proglottis from the dog's 

 bowels and get into the water. On entering 

 the herbivorous or omnivorous host the ova 

 hatch, and the embryos make their way via 

 the portal system to the liver. They there 

 produce a small white cyst, which contains a 

 vesicle. Development proceeds very slowly. 

 By the end of five months, Leuckart has shown that they attain 

 the size of a walnut. They now consist of a whitish-yellow 

 vesicle with thick walls composed of two layers (fig. 15) 

 — the outer one thick, and called the hydatid membrane 

 (ct) ; the inner one thin (m), and known as the germinal 

 membrane. Internally this " mother - vesicle " contains a 

 colourless neutral fluid. In some cases the "mother-vesicle" 

 remains in this state, no scolices being produced, when it 

 is called an " acephalocyst." Should further development 

 take place, as is usually the case, a number of buds close 

 together arise from the germinal layer (vp). These buds 

 become hollow, and from their internal walls scolices appear. 

 As many as thirty scolices may be formed in each of these 



Pig. 14. — T.EN1A 



ECHINOCOCCUS. 



A. Hook from same. 



