94 BOARD" OP AGRICULTURE. 



branes. As long as these cysts remain in a living animal, 

 new heads are constantly formed, by their peculiar methods 

 of budding, and when new cysts are formed either within or 

 outside of the older ones, they develop on their inner mem- 

 branes other heads in the same way, so that if the sheep or 

 other animal lives long enough to develop a large tumor, it will 

 finally contain many thousands of these minute tape-worm 

 heads. In examining one of these tumors taken from a dead 

 animal, most of the heads and also the internal secondary cysts 

 are usually found floating freely in the watery fluid in great 

 numbers, giving it a turbid appearance, and on standing they 

 settle to the bottom as a granular sediment. This is 

 due to changes after the death of the parasite, though some 

 of the secondary cysts may be free during life. 



Development. 



Now, if a dog eats the liver, lungs, kidney, or other parts 

 containing such tumors, and swallows either the cysts or the 

 detached heads, these will lose the enclosing membrane, stems, 

 and other parts that are no longer useful, the heads with their 

 suckers and hooks will be protruded, and, passing into the 

 dog's intestine, each one will fasten itself by means of the 

 hooks and suckers to the soft membrane lining the intestine. 

 In this situation they remain and soon develop a small body, 

 having only three separable sexual joints, as shown in Figure 

 70, which represents the mature tape- worm {Tcenia echinococ- 

 cus) greatly magnified. This tape-worm never becomes long, 

 with hundreds of joints, as do the pork and beef tape-worms of 

 man. It is only about an eighth of an inch long when ma- 

 ture. The last joint, which is much the largest, contains both 

 male and female organs, and is perhaps capable of self-impreg- 

 nation ; it is therefore a complete hermaphrodite. After this 

 has matured and discharged its eggs, the two next in turn de- 

 velop their sexual organs and take its place. In Figure 70 

 the male organ may be seen projecting from one side, and the 

 ovaries, containing many eggs, occupy the bulk of the 

 joint. The eggs pass out through a duct that opens by 

 the side of the male organ, and each egg is fertilized 

 before being discharged. Thousands of these little tape- 

 worms, derived from one large cyst, often live together in 



