510 ENTOZOA. 



gitudinal stria, and finely striated transversely. No external organ what- 

 ever is perceptible, and internally we find nothing but the ova, variously 

 distributed in the length of the parenchyma. 



They inhabit the abdomen of certain Birds, and particularly of various 

 fresh-water Fishes, enveloping and constricting their intestines to such a 

 degree as to destroy them. At certain periods they even perforate the 

 parietes of their abdomen to leave it. One of them, the 



L. abdominalis, Gm., inhabits the Bream. In some parts of Italy these 

 worms are considered agreeable food. 



CLASS III. 

 ACALEPHA.(l) 



Our third class comprises Zoophyta which swim in the waters of 

 the ocean, and in whose organization we can still perceive vessels, 

 which, it is true, are generally mere productions of the intestines 

 excavated in the parenchyma of the body. 



ORDER I. 



SIMPLICIA. 



The simple Acalepha float and swim in the ocean by the alternate 

 contractions and dilatations of their body, although their substance 

 is gelatinous and without any apparent fibres. The species of ves- 

 sels observed in some of them are hollowed out of their gelatinous 

 substance; they frequently and evidently originate from the stomach, 

 and do not occasion a true circulation. 



Medusa, Lin. 

 The Medusae are furnished superiorly with a disk more or less convex, re- 

 sembling the head of a mushroom, and called the umbella. Its contractions 



(1) Nettles, from aic«x*f». 



