CHAPTER IV. 



BfiANt ii IV. E( binodebmai \. (Slar-J rchins, 



eri 



General Characters of Echinoderms. Wenowco 

 to animals of much more complicated structure than 

 of the foregoing branches, and in which the radiated ar- 

 rangement of the parts of the body is in mos 

 marked aa the jointed or ringed structure of worms 

 insects; f<>r not only arc the body-walls of the star fish or 

 sea-urchin, or even many <»f the Bolothurians (though less 

 plainly), divided into five wedge-shaped portions, or pro- 

 duced into five arms as in the common star-fish or Kve- 

 finger, but the nervous system, the reproductive organs, 

 blood and water-vascular systems, and the locomotive 

 organs, are usually arranged in accordance with the star- 

 like form of the body. The most trenchant character which 

 separates the Echinoderms from the Coelentcrates, and 

 allies them to the worms, is the genuine tube-like dig 

 canal which lies free in the body-cavity, aud may be 

 oral or many times the length of the body. 



The studenl can gain a correct idea of ibe £ ' the 



Echinoderms from a careful examination of the common star-fisb 

 ia» vulgarix), which is the most common and accessible Ecliiuo- 

 derra to be found on the New Euglund sbon - 



fish iii some a a water and noticing - n-. the thrusting out of 

 the ambulacra] feel or suckers by whicb it pulls or «:iv imsy 



r tin' mussel-beds, or reck-, or the arms 



ble of slightly bending; aftei ring the red eye spot at ih< 



of each arm or ray, and the m< tvements of the numerous spine a w 

 are attached by a Bort of bad and-sockel joint to the c is frame- 



work of the body-walls, and examining the movemi i 

 ified spines calli . inch arc piuccr- 



