THE STARFISH. 



267 



upturned arm note that these spring from a groove which 

 extends along the lower side of the arm its entire length. 

 Observe that these tube feet are pushed out and drawn in 



STARFISH. 1. Starfish (Asterias vulgaris), a large dried specimen one half 

 natural size. 2. Diagram of cross section of oral part of an arm : br, 

 branchial tentacle ; sk, calcareous plate of skeleton (in heavy black) ; sp, 

 spines (those designated are on an adambulacral plate); amp, ampullae; 

 c, radial canal; n, radial nerve; amb, ambulacra, or tube feet. 3. Dia- 

 gram of water-vascular system: ra, madreporite; sc, stone canal; coc, cir- 

 cumoral canal; re, radial canal; amp, ampullae ; amb, ambulacra. 

 4. Starfish infolding an oyster preparatory to eating it. 5. Diagram of 

 parts of digestive and reproductive organs, etc.: st, stomach; h, hepatic 

 caeca ; o, ovaries ; amp, ampullae ; ambp, ambulacral plates as seen when 

 ampullae are removed. 



and turned about freely, and that in locomotion they are 

 advanced in the direction in which the animal is moving, 

 attached by means of terminal disks, and then contracted, 



