PARASITES OF ANIMALS. 87 



to correspond to one of the withdrawn and inverted worms, 

 as represented in Figure 64. 



Each little worm has a head with a circle of hooks in the 

 middle, surrounded by four suckers, just as in the measle- 

 worm of pork. In this case, each little worm with a head is 

 the larva of one of the dog tape-worms (Tcenia caenurus), 

 hut in this the young worms have the power of propagating 

 themselves by a kind of budding, in a manner similar to that 

 by which the coral-animals bud from each other and so 

 build great colonies. Thus it is that one of these little 

 worms, lodged in the brain, by budding produces hundreds of 

 others like itself, all connected together by the membrane of 

 the sac ; and thus the tumor constantly grows larger, instead 

 of always remaining small, as does the measle-worm. 



Effects. 



Now, if a dog gnaws a skull containing such a tumor, and 

 swallows the whole cyst, or any part of the membrane that 

 has heads on it, the heads will be liberated from the mem- 

 brane, and each one will fasten to the lining of the dog's 

 intestine by means of its suckers and hooks. There they will 

 rapidly grow larger and larger ; new joints will be formed for 

 the body, and in the course of three months each one will become 

 a small tape-worm, with many joints, and each of the larger 

 joints will have both male and female organs, and will be 

 capable of propagating the race by itself. The female organs 

 of each joint contain thousands of eggs, which are discharged 

 when mature, and passing from the intestine of the dog in 

 large numbers, they will be scattered about freely over the 

 pastures and fields wherever the dogs go. If a lamb or sheep 

 accidentally swallows some of the eggs with grass or in water, 

 the eggs will hatch in the stomach into minute worms. These 

 force their way, by means of their six little hooks, through 

 the lining of the intestine into the blood-vessels, and are thus 

 carried to different parts of the system ; but usually only 

 those that lodge in the brain live, and there excavate galleries 

 (Figure 65) and grow, and bud, thus forming the " water- 

 brain," and finally kill the sheep. Ccenurus cysts have been 

 observed, however, beneath the skin of sheep, in the cellular 

 tissue. Similar cysts have, also, been found in the liver 



