284 SYSTEMATIC ZOOLOGY. 



tures. Along our shores two groups or orders occur: 

 PEDATA, in which there are ambulacra and branchial trees; 

 and APODA, in which both these structures are lacking, 

 and the body is decidedly worm-like. 



The food of the holothurians consists largely of organic 

 matter in the sand or mud on which they live. The ten- 

 tacles are used to push the sand into the mouth. 



SUMMARY OF IMPORTANT FACTS. 



1. The ECHINODERMA have a calcareous integument in 

 which spines are frequently developed. They have both 

 radial and bilateral symmetry, the latter primitive. All 

 are marine. 



2. They have a complete alimentary canal, with both 

 mouth and vent, distinct from the large body-cavity. 



3. They have an ambulacra! system consisting of madre- 

 porite, stone-canal, ring-canal, radial canals, ampullae, and 

 ambulacra. In many this serves for locomotion. 



4. The body surface can be divided into ambulacral, 

 interambulacral, and adambulacral areas. 



5. The Echinoderms possess marked powers of regener- 

 ating lost parts. 



6. They reproduce solely by means of eggs. The young 

 undergo a metamorphosis in reaching the adult condition. 



7. The Echinoderma are divided into Asteroidea, Ophiu- 

 roidea, Crinoidea, Echinoidea, and Hplothuridea. 



8. The ASTEROIDEA are star-shaped, without marked dis- 

 tinction between rays and disc; the radial canals and 

 nerves are external to the calcareous ambulacral plates. 



9. They are very destructive to molluscs. The stomach 

 is protruded from the body in order to digest the prey. 



10. The OPHIUROIDEA differ from the Asteroidea in 



