70 



SIR C. WIVILLE THOMSON ON THE MODE OF 



gastraea cavity ; and a wbitisli spot with a slightly raised border 

 indicates an opening which, I have no reason to doubt, is the per- 

 manent mouth ; but of this I cannot be absolutely certain. The 



Fig. 9. 



'^^; 



Hemiaster, sp. The arrangement of the eggs in one of the marsupial recesses. 

 Fiye times the natural size. 



surface now assumes a translucent appearance, and becomes deeply 

 tinged with dark purple and greenish pigment ; and almost imme- 

 diately, without any definite intermediate steps, the outer wall is 

 filled with calcified tissue, it becomes covered with fine spines 

 and pedicellarise, a row of tentacular feet come into action round 

 the mouth, the vent appears at the posterior extremity of the 

 body, and the young assumes nearly the form of the adult. These 

 later changes take place very quickly ; but they are accompanied 

 by the pi eduction of so much heavy purple and dark-green pig- 



