PARASITIC WORMS. 



: CHAPTER VIII. 

 PARASITIC WORMS. ENTOZOA.* 



LAVISHLY as we have already found the world to be filled 

 with the lower forms of animated beings, our astonishment 

 will be by no means lessened when we learn that innumerable 

 creatures have been ordained to lead a parasitic life, and to pro- 

 cure their nourishment from the superabundant juices of other 

 animals; neither is this race of parasites by -any means deficient 

 in numerical importance, or constructed with less careful adapta- 

 tion to the situation in which they are destined to reside. They 

 present, however, little to invite our attention, and the details 

 known concerning their general economy are, as yet, extremely 

 few and unsat'sfactory 



One of the most common is 



The Hydatid (Cysticercus), 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 con- 

 sisting of a double row of recurved 

 spines and four adhesive suckers 

 represented upon an enlarged scale 

 upon the right-hand side of the figure. 

 These simply-constructed animals, for- 

 merly regarded as a distinct species, 

 have been proved by recent experi- 

 ments to be but an incomplete con- 

 dition of 



The Tape- Worm's (Tenicc\ many 

 species of which are met with in the aliment- 

 ary 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, sometimes 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 Fluke (Distoma hepaticum}, but too well known as inhabiting the liver 

 of the sheep, will serve as an example. It resembles in shape a little sole, 



FIG. 52. CYSTICERCUS. 



* eiros, entos, within ; faov, zoon, an animal. 



