§ 37. CRINOIDEA. OR LILY-SHAPED ANIMALS. 645 



of animals, is secreted by a membranous structure, and that 

 if tlie lime be removed by a chemical process, the tissue will 

 be rendered manifest. Few, however, will be prepared 

 to learn, that even in corals which have been entombed 

 in the solid rock for innumerable ages, the animal mem- 

 brane can be detected. To my late friend, Mr. Parkinson, 

 we are indebted for the knowledge of this interesting fact. 

 He immersed a piece of marble (Lign. 143, fig!, 2) in 

 dilute muriatic acid, which has the property of dissolving 

 calcareous earth, but cannot affect animal matter : to em- 

 ploy his own words, 6i as the calcareous earth dissolved, 

 and the carbonic acid gas escaped, I was delighted to 

 observe the membranous substance depending from the 

 marble in light flocculi, of a deep red colour ; and although 

 not retaining the tubular form of the original coral, yet 

 appearing in a beautiful and distinct manner."* 



37. Crlnoidea, or Lily-shaped axemaxs. f — The 

 Echinites, so numerous in the chalk (ante, p. 327), and the 

 Star-fishes, which are more sparingly distributed in the 

 cretaceous strata (ante, p. 327), are referable to the same 

 group of marine animals as those to which I would now 

 direct your attention. All these creatures belong to the 

 class Radiaria, so named from the different parts of which 

 they are composed being arranged symmetrically around 

 one common centre. This structure is exemplified in 

 the Asterias, or Star-fish, that abounds on our coasts, 

 and must be familiar to every one. This animal has a 

 central disk containing the mouth and viscera, from 

 which proceed five long arms, or rays; the skeleton is 

 composed of numerous little bones, enveloped in a tough 

 integument. These bones, or ossicula, are calcareous ; 

 and are in close apposition over the body, but are articu- 



* Organic Eemains of a Former World, vol. ii. p. 181. PL I. 

 fig. 3. 



f Medals of Creation, chap. ix. 



u u 2 



