COKALS FORM AND ACHIEVEMENTS, 139 



remainder being covered with the common gelatinous 

 envelope to which they are attached, or rather from 

 which they proceed. If a transverse section be made of 

 a branch of Coral, it will be seen to have some resem- 

 blance to the porcupine quill, or the spine of the sea- 

 urchin, the lines of the corrugated surface being con- 

 tinued inwards until they nearly meet in the centre. 



A SECTION OF COIIAL. 



The preceding illustration shows the transverse section 

 as it appears when ground down and polished, so as to 

 be placed under the microscope. 



The ordinary appearance of the polypes, when 

 extended and withdrawn, is shown in the illustration on 

 next page. 



One of them is represented as fully extended, and 

 standing out boldly from the general mass, its eight 

 fringed tentacles fully extended for the capture of food. 



