472 ENTOZOA. 



but even the cellular tissue, and the parenchyma of the most com- 

 pletely invested viscera, such as the liver and brain. 



The difficulty of conceiving how they get there, added to the fact of 

 their never having been seen out of living bodies, has induced some 

 naturalists to believe that they are spontaneously engendered. We 

 now know that most of them not only produce ova or living young 

 ones, but that, in many, the sexes are separate, and coition ensues 

 as among other animals. We are then compelled to believe, that 

 they propagate their race by germs sufficiently minute to be trans- 

 mitted through the narrowest passages, and that frequently those 

 germs are contained in animals at birth. 



In the Intestinal Worms we find neither tracheae, nor any other 

 organ of respiration, and they must receive the influence of oxygen 

 through the medium of the animal they inhabit. They present no 

 trace of a true circulation, and we merely perceive vestiges of nerves 

 so extremely obscure, that many naturalists have doubted their 

 existence *. 



When those characters are found united in an animal with a form 

 similar to that of this class, we place it here, although it may not 

 inhabit the interior of another species. 



The injury caused by worms to animals, in which they become exces- 

 sively multiplied, is well known. The most efficacious agent for 

 destroying those of the alimentary canal seems to be animal oil mixed 

 with spirits of turpentine t. 



We will divide the Entozoa into two orders, which are perhaps suf- 

 ficently different in organisation to form two classes, if we had the 

 observations requisite to determine their limits. These orders are the 



ENTOZOA NEMATOIDEA, Rudolphi, 



Which have an intestinal canal floating in a distinct abdominal cavity, 

 a mouth and anus ; and the 



ENTOZOA PARENCHYMATA J, 



Where the parenchyma of the body contains obscurely terminated vis- 

 cera, most commonly resembling vascular ramifications, and sometimes 

 not visible. 



" For the anatomy of these Worms, besides the Entozoa of Rudolphi, see the Mem. 

 of M. Otto, 8oc. Nat. Berl., 1816, and the work of M. J. Cloquct. 



f See Cliabcrt, Traite des Maladies Vermincuscs, and Rudolphi, i. p. 493. 

 J They comprise the tour last orders of Rudolphi. 



