Survey of the Animal Kingdom 301 



autos, self; tome, cutting or mutilating) (Fig. 28). The eggs of many species 

 lend themselves admirably for experiments on artificial parthenogenesis (develop- 

 ment of the egg without fertilization). Number of species of Echinodermata, 

 6,000. 



Classification of the Phylum Echinodermata 



Glass 1 — Asteroidea (as ter -oi' de a) (Gr. aster, star; eidos, resemblance). — 

 These are typically free-living, five-rayed (pentamerous) types with the five rays 



Ambulacral Braces 

 (Skeletal) 



Hepatic Caeca — 



Ampullae of 

 Tube Feet 



yr;>y, :'::^'"'*-~~r-^- '^i,^,r-_^<^^^^^ £ toiTia ch 



(Pyloric) 

 ^-Rectal Caeca 



Duct to 



Radial Canal 



Eye 



Fig. 105. — Common starfish (Asterias forbesi) dissected from the aboral sur- 

 face to show the digestive, locomotor, reproductive, and skeletal systems. I, Arm 

 or ray, showing aboral surface covered with spines; // and III, arms with aboral 

 surface removed; IV, arm with aboral surface removed and the hepatic caeca 

 moved to show the bulblike ampullae of the tube feet, etc.; V, arm with internal 

 organs and vertebral ridge removed to show the four rows of ampullae of the 

 tube feet, the connecting canals, and the radial canal (all of the water vascular 

 system). 



