Descriptive Zoology. 



GENERAL CHARACTERISTICS OF ECHINODERMATA. 



1. The body and its various organs are radially arranged. 

 But many show more or less bilateral symmetry. 



2. In their development they all undergo a marked meta- 

 morphosis, the young being bilaterally symmetrical, and 



only in a later stage acquiring 

 the radiate arrangement. 



3. The surf ace has an exoskel- 

 eton of calcareous plates, with 

 movable spines. 



4. There is a well-developed 

 digestive tube, distinct from the 

 body cavity. 



5. There is a peculiar system 

 of water tubes by which tube feet 



are extended and locomotion effected in the 

 free forms. 



6. They reproduce by means of eggs, and 

 do not bud. 



7. They do not occur in colonies. 



8. They are all rather sluggish. 



9. They are all, without exception, 

 marine. 



10. They have remarkable power of 

 regeneration after mutilation. 



The echinoderms were formerly 

 classed with the ccelenterates on ac- 

 count of the radial arrangement of the 

 parts of the body ; but the echinoderms differ sharpb 

 from the ccelenterates in having a digestive tube distinc 

 from the body cavity, and in having a much higher devel 

 opment, as shown in the variety and perfection of the 



FIG. 195. STONE LILY 



(CRINOID). 

 From Packard's Zoology, 



