26 ELEMENTS OF COMPARATIVE ZOOLOGY. 



capsule, where they remain indefinitely. If this infested 

 flesh be eaten raw, the capsule is dissolved by the stomach, 

 the young are soon born, and they in turn wander through 

 the muscles, and, when numerous, this boring into the flesh 

 causes severe sickness, and even death. The worst epidemic 

 of this disease, known as trichinosis, on record occurred 

 near Emmersleben, Saxony, in 1884. From one pig three 

 hundred and sixty-four persons were infected, and of these 

 fifty-seven died within a month. The moral which we 

 have to learn from tapeworms and trichina is that our 

 beef and pork should never be eaten raw, but should be 

 cooked through. 



CLASS III. ANNELIDA (p. 239). 

 CLASS IV. MOLLUSCOIDEA. 



Under this heading are grouped a few forms, which in 

 time past were considered as Molluscs (see p. 269), but 

 which are now known to have only superficial resemblances 

 to the clams, etc. There are two orders of these Mol- 

 luscoids. 



OKDER I. POLYZOA (Moss Animals). 



The Polyzoa are individually small, but by budding they 

 form colonies of considerable size, the tentacles of the in- 

 dividuals giving the colony a mossy appearance. These 

 tentacles surround the mouth in a more or less modified 

 circle, and by them the animals obtain their food. The 

 body is sac-like, and the alimentary canal is bent upon 

 itself so that the vent is near the mouth. Many of the 

 colonies secrete an external skeleton, which may be horny 

 or calcareous. Most of the Polyzoa are marine, but a few 

 occur in fresh water. 



