ENTOZOA. 75 



known concerning their general economy are, as yet, 

 extremely few and unsatisfactory. 

 One of the most common is 



The Hydatid {Cysticerciis), which not unfrequently infests the 

 flesh of pigs, causing that diseased condition which is known as 

 measly pork. Its body consists of a globose transparent bag, with a 

 slender neck, terminated by a remarkable prehensile apparatus — 

 consisting of a double row of recurved spines and four adhesive 

 suckers— represented upon an enlarged scale upon tlie riglit-hand 



Fig. 52.— riGUEE oi cisticeken. 



side of the figure. These simply-constructed animals, formerly re- 

 garded as a distinct species, have been proved by recent experiments 

 to be but an incomplete condition of 



The Tape-worms {Tenix), many species of which are met with 

 in the alimentary canal of various animals, where they have been 

 known to attain the length of sixty, or even a hundred feet. The 

 body of the tape-worm consists of a great number of segments, some- 

 times amounting to five hundred or more ; these become very slender 

 as they approach the so-called head (scolex), from which they are 

 all successively produced. 



The Flukes [Distoma) constitute a very numerous race, of which 

 the Liver Fliihe, Distoma liepaticum, but too well known as inhabit- 

 ing the liver of the sheep, will serve as an example. It resembles in 

 shape a little sole, about an inch in length, furnished with two 

 suckers, each of which was at one time supposed to be a mouth — 

 whence the origin of their name. WJien sheep are pastured in low 

 wet meadows, this animal often multiplies in them excessively, 

 producing dropsy or rot, and finally causing the death of the poor 

 creatures so infested. 



E 2 



