PENTACRINUS. ENTOZOA. ^ 405 



Gen. PENTACRINUS, Thompson. 



Pelvis of five plates, supporting five costals ; column not en- 

 larging at the summit ; fingers formed of a single series of 

 joints; column pentagonal, the articulating surfaces of the 

 columnar joints petal-shaped. 



P. EuropcBtts, Thomp. Arms ten, nearly simple ; axillary side arms 

 five, at the summit of the body. Found in the Cove of Cork, 

 Ireland. Fleming, Brit. Anim. 493. 

 Numerous remains of extinct animals of this family occur in the limestones of 



Britain. 



CLASS XL ENTOZOA, Rud. Fermes, Lam. 



Body soft, elongated, naked in almost all, without head, eyes, 

 or feet; mouth formed of one or many suckers ; no tenta- 

 cula or organs of respiration ; intestinal canal in some 

 scarcely perceptible. 



THE intestinal worms are remarkable for existing and pro- 

 pagating only in the interior of other animals. There is scarce- 

 ly an animal in which there are not found some species of pa- 

 rasitical worm ; and they occur not only in the alimentary canal 

 and the vessels which communicate with it, such as the he- 

 patic vessels, but even in the cellular tissue, in the liver, and 

 the brain. The difficulty of conceiving how they appear in 

 these parts, joined to the observation, that they are never found 

 but in living bodies, had led some naturalists to suppose that 

 they were engendered spontaneously. It is, however, now ascer- 

 tained, not only that the greater part produce ova or living 

 young, but that many have separate sexes, and couple as ordinary 

 animals. These germs or ova, however, must be of extreme mi- 

 nuteness to be able to pass through channels so narrow. 



The intestinal worms being destitute of trachea, branchiae, or 

 any other organ of respiration, must necessarily acquire oxygen 

 through the medium of the animals which they inhabit. No 

 traces of circulating vessels have been detected ; and the vesti- 

 ges of nerves are so obscure, that many naturalists have doubt- 

 ed their existence. When these characters are found in an animal 



