VARIOUS FOKMS OF TAPEWORMS. 51 



dung-heap. If a pig happens to come across them they are 

 speedily eaten, and hundreds of the contained ova are dehisced 

 into the stomach, and give rise to the typical six-hooked cestode 

 embryos. These enter the vascular system in swarms and take 

 up their ahode in the muscles, or rather in the connective tissue 

 between them. Sometimes they even reach the brain and spinal 

 cord, and may also be found in adipose or fat tissue. These 

 embryos form small watery cysts about the size of peas, especi- 

 ally in the loins, and give rise to the disease in pigs known as 

 "measles." From ten to twenty thousand cysts (fig. 13, c) have 

 been counted in one pig. Should this " measly pork," which is 

 condemned in the markets in England, be eaten by man, each 

 one. of those cysts wiU become converted into the obnoxious 

 human pest, Tcenia solium. The cystic stage is also said to be 

 found in man in his eyes, brain, and muscles. The disease is 

 stiU persistent in some C!ontinental districts and in Ireland ; but, 

 owing to our more sanitary ways of living, its effects are being 

 less felt than formerly. It is a disease that has been observed 

 for a very long period, being well known, although not under- 

 stood, by the ancients. 



EcMnococeus. — A third type of cyst known as Echinococcus 

 often assumes a great size. The sexual tapeworm that produces 

 this cyst is Tmm'a echinococcus (Sieb.), fig. 14. This worm is 

 found in the dog, and is very prevalent. It is minute in size, 

 seldom exceeding one-fifth of an inch in length, and is composed 

 of never more than four elongated segments. The last segment, 

 which is much the largest, contains numbers of ova when 

 mature. The head is provided with a double row of 

 hooks. The colour is creamy-white, and they may be found in 

 great numbers in the fluid contents of the dog's intestines, and 

 are often seen sticking round the anus. These worms are 

 derived from the cysts known as EcMtiococcus veterirwrum, found 

 in herbivorous animals and man, but especially in the Euminants. 

 The worms reach maturity in about a month after the entry of 



