R ADI ATA. 185 



mates three hundred thousand such muscles in a single 

 Pentacrinus an amount of muscular apparatus far ex- 

 ceeding any that has been elsewhere observed in the 

 animal creation. The family, COMATULlDyE, or Hair- 

 stars sometimes termed Feather-stars in their young 

 condition, resemble the Encrinites, or Sea- lilies, being 

 supported on a long flexible stalk, composed of calcare- 

 ous cylinders. At maturity they quit their attachment, 

 and crawl about like other Star-fishes. 



The order ASTEROIDEA, or Star-fishes, consists of ani- 

 mals with a flat central disk, having five or more arms, 

 or lobes, radiating from it, and containing branches of 

 the viscera. The skin is leathery, hardened by small 

 calcareous plates, (eleven thousand or more,) but some- 

 what flexible. The mouth is below, and the rays are 

 furrowed underneath and pierced with numerous holes 

 through which pass sucker-like tentacles for locomotion 

 and prehension. These furrows are named ambulacra, 

 or avenues, from a fancied resemblance to a walk, or 

 alley, in a garden. As the tentacles, or suckers, are only 

 protruded from these spaces, they also have been called 

 ambulacra. The arrangement for their protrusion will 

 be described in connection with the Sea-urchins, as well 

 as the Pedicellaria (formerly believed to be parasitic or- 

 ganisms) found near the mouth. 



About one hundred and fifty species of Star-fishes are 

 known, divided into three groups: (i.) those having four 

 rows of feet, as the common five-fingered Star-fish, or 

 Asterias ; (2.) those with two rows, as the many-rayed 

 Solaster, or Sun-fish, and the pentagonal Goniaster ; 



(3.) those with long slender arms, which are not prolon- 

 16* 



