106 



HITCHCOCK'S ANATOMY. 



external skeleton highly calcareous. In the Asteroidea there 

 is also an internal articulated skeleton. The structure of 

 these skeletons is too complicated for description here. The 

 Echinidae are remarkable for calcareous knobs and rays, both 

 sharp and blunt, sometimes several inches long ; hence this 

 common name, Sea Hedge-Hog, or Porcupine. 



Skeletons of the Protozoa. — The organisms brought 

 together by Prof. Owen under Protozoa, are the Amorphozoa 

 or Sponges, the Foraminifera, and Infusoria, " which, 93 he 

 says, " manifest the common organic characters, but without 

 the distinctive super-additions of true plants or animals." Of 

 the skeletons of the Infusoria we know little, save that they 

 occur fossil, and are composed of silica and iron ore. 



The Foraminifera are small, gelatinous animals, protected 

 by a calcareous shell. The Sponges are said to be ceratose 

 or horny* siliceous or flinty and calcareous or limy, accord- 

 ing as their frame- work partakes of these several characters. 



What is said of the skeletons of the Protozoa? What of the Forminifera? 



