1 84 THE SCIENCE OF LIFE. 



of the body. In the day-time its waving cilia along the 

 margins of the body glitter with the tints of the rainbow, 

 and at night it appears like a long waving flame in the 

 water. 



5. The subtype of Radiate animals, called ECHINO- 

 DERMATA, is distinguished by the possession of a nervous 

 system, in the form of a pentagonal ring round the 

 mouth ; an alimentary canal, with oral and anal aper- 

 tures ; a peculiar system of circular and radiating canals ; 

 and a symmetrical arrangement of all the parts of the 

 body around a central axis, in multiples of five. Some 

 star-fishes (Solaster) have twelve rays. In all Echino- 

 derms, probably, sea-water is freely admitted into the 

 body-cavity around the viscera. The canals likewise 

 contain water, which enters through a porous tubercle, 

 the madreporic plate, or dorsal wart, best seen on the 

 back of the star-fish and the sea-urchin. Some natural- 

 ists rank Echinoderms as Worms. 



The Crinoidea, or Sea-lilies, so called from their re- 

 semblance to flowers, are fixed to the sea-bottom by a 

 hollow, jointed, flexible stem, which carries the body, 

 which is cup-shaped, with radiating arms, or tentacles. 

 This order includes an immense number of fossil forms, 

 but deep-sea dredging has brought up many living 

 species, formerly thought to belong exclusively to the 

 Mesozoic period. They all possess an internal skeleton 

 of infiltrated calcareous matter, so that the entire animal 

 consisted of thousands of stellate pieces, or joints, con- 

 nected by animal matter. As each joint is furnished 

 with at least two bundles of muscular fiber, one for ex- 

 tension and one for contraction, Dr. Carpenter esti- 



